Polyaxial Screw

ABSTRACT

The present invention generally is directed toward a spinal fixation system whereby a coupling element allows the physician to selectively lock or unlock either the connection between the coupling element and a fastener, such as to allow for repositioning of the coupling element, or the connection between the coupling element and an elongate rod. The locking or unlocking of these connections may be made independently and as desired by the physician.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. Ser. No.13/967,075, filed Aug. 14, 2013, which is a continuation application ofU.S. Ser. No. 13/911,801, filed Jun. 6, 2013, which is a continuation ofU.S. Ser. No. 13/887,098, filed May 3, 2013, which is a continuationapplication of U.S. Ser. No. 11/294,389, filed Dec. 6, 2005, now U.S.Pat. No. 8,475,495, which is a continuation-in-part application of U.S.Ser. No. 11/146,147, filed Jun. 7, 2005, now U.S. Pat. No. 8,034,086,which is a continuation-in-part application of U.S. Ser. No. 10/819,994,filed Apr. 8, 2004, now U.S. Pat. No. 7,503,924, the entire contents ofwhich are incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to orthopedic fixation devices comprisinga rod and a bone screw having a variable angle head. The variable anglehead of the bone screw has a coupling element that can independentlylock the angulation of the head relative to the screw axis and securelyprevent movement of the rod within the variable angle head.

BACKGROUND OF THE INVENTION

Many types of spinal irregularities can cause pain, limit range ofmotion, or injure the nervous system within the spinal column. Theseirregularities can result from, without limitation, trauma, tumor, discdegeneration, and disease. Often, these irregularities are treated byimmobilizing a portion of the spine. This treatment typically involvesaffixing a plurality of screws and/or hooks to one or more vertebrae andconnecting the screws or hooks to an elongate rod that generally extendsin the direction of the axis of the spine.

Treatment for these spinal irregularities often involves using a systemof pedicle screws and rods to attain stability between spinal segments.Instability in the spine can create stress and strain on neurologicalelements, such as the spinal cord and nerve roots. In order to correctthis, implants of certain stiffness can be implanted to restore thecorrect alignment and portion of the vertebral bodies. In many cases, ananchoring member such as a pedicle screw along with a vertical solidmember can help restore spinal elements to a pain free situation, or atleast may help reduce pain or prevent further injury to the spine.

Some systems are directed toward immobilization of the vertebral bodiesby implantation of bone screws, couplings, and elongate rods. Examplesof such systems include U.S. Pat. Nos. 5,690,630, 5,669,911, and5,672,176. It is well known that difficulties can arise during asurgical procedure when attempting to connect a vertical solid member,such as a rod, to a bone screw. As a result, it may be desirable to usea variable angled coupling element to connect a rod to a bone screw.This lessens the need to modify the system, such as by bending the rod,by repositioning the screw, or the like. The coupling element acts as anelbow which can “reach out” to the rod and allow for easier adjustmentand installation of the rod in the patient.

Typically, a conventional polyaxial screw described by the prior artoften has a cap of some kind is used to compress the rod onto thecoupling element. This compression of the rod enables the lockingmechanism within the coupling element to fix the angle between the bonescrew and said element. Therefore, the vertical compression of the rodis paramount in the design of the bone screw system.

Conventional polyaxial screws also typically require that compression ofthe coupling element and the bone screw be achieved through the clampingof some form of taper within the coupling element. This is achievedusually by means of slits which are placed within the members of thecoupling element. When these elements are placed in compression thetines created by the slits contract on the head of the screw by means ofa cylindrical taper. In addition to the references mentioned above,additional examples of such systems requiring pressure from the rod tolock the position of the polyaxial screw head also can be found in U.S.Pat. Nos. Re 37,665, 5,733,286, and 5,476,464. Some systems, such asdescribed in U.S. Pat. No. 6,248,105, describe the possibility ofseparately fastening the connecting body to the spherical head andelongated rod.

While these designs may provide an advantage of reducing assembly timeover earlier screw designs by requiring clamping of only one fastener tohold the rod and coupling element by applying pressure against the headof the bone screw, such systems lack the ability to separately unlock orrelease one element, such as the rod or the coupling element.

SUMMARY OF THE INVENTION

The present invention is generally directed towards an improvedanchoring system using a polyaxial screw that is capable ofindependently affixing a coupling member to the screw head while alsopermitting an elongate rod to be held securely in a desired position.

In general, the present invention may be used in a variety of spinestabilization systems. For instance, one embodiment has an elongate rod,a bone fastener having a rounded or semi-spherical head, a couplingelement, and a skirt having an interior space for receiving the fastenerhead and coupling element. The coupling element may be formed of onepiece or may comprise a plurality of connectors. A plurality of stopsmay be disposed on the coupling element or on the plurality ofconnectors, which may be configured and adapted to slidingly communicatewith a coupling ring having one or more arms extending toward thefastener. The arms of the coupling ring may be selectively engaged withthe stops to lock the position of the skirt with respect to the positionof the fastener. Some embodiments of the present invention furthercomprise a cap capable of engaging with a first end of the skirt andcapturing the elongate rod within a recess, channel, or opening in theskirt when the cap is rotated to a first position relative to the skirt.

In one embodiment, the cap is capable of rotating to first and secondpositions relative to the skirt. Rotation of the cap relative to theskirt may cause the cap to press the elongate rod toward the couplingring so that the coupling ring arms apply pressure against the pluralityof stops and lock the skirt in position relative to the bone fastener.

In another embodiment, the cap comprises a locking element capable ofsecurely holding the elongated rod in a fixed position relative to theskirt. The cap also may have a threaded opening and the locking elementmay be a threaded set screw disposed within the threaded opening.Preferably, the set screw is capable of applying downward pressure onthe elongate rod to lock the elongate rod in position relative to theskirt.

In still yet another embodiment of the invention, the cap and skirt mayhave at least one detent or protrusion and corresponding recess ordepression that contact each other when the cap is in its secondposition to resist inadvertent loosening of the cap from the skirt. Thisfeature may be particularly beneficial if a set screw or other lockingelement is used in the cap to selectively lock or unlock the elongaterod. Depending upon its configuration, rotation of the cap toward to thefirst or second position may cause the detent and corresponding recessto provide a tactile or audible signal to the physician. In someembodiments, a plurality of detents and recesses may be provided foreach predetermined position of the cap relative to the skirt. Thus, inone embodiment, rotation of the cap to a first position relative to theskirt causes the cap and skirt to provide a tactile or audible signal,such as a click, to the physician. Moreover, in some embodimentsrotation of the cap to a second position relative to the skirt resultsin a tactile or audible signal to the physician.

In some embodiments, the cap comprises a sidewall having a first andsecond channel formed therein. The first and second channels may bewider than the diameter of the elongate rod so as to allow some rotationof the cap without obstruction by the elongated rod. In one embodiment,the first and second channels are configured to permit the cap to rotatefrom 5° to 90° when in communication with the skirt without beingimpeded by the elongate rod. In yet another embodiment, unimpededrotation of the cap is from about 20° to about 40° when in communicationwith the skirt and with the elongate rod.

The cap may be capable of rotating up to about 30° before reaching thefirst position. Moreover, the cap may be configured to provide a tactileor audible click when rotated to the first position. In addition, atleast one channel in the cap sidewall may comprise a cammed upper edgethat is capable of urging the elongate rod toward the coupling ring asthe cap is rotated. Moreover, in one embodiment the skirt may have aplurality of threads capable of engaging with the cap and drawing thecap toward the elongate rod as the cap is rotated.

Additionally, bone fastener head may be textured with helical grooves orhave some other textured surface. In one embodiment, a first connectorhas a first textured surface, a second connector has a second texturedsurface, and the first and second textured surfaces contact the roundedhead when the coupling element is locked to the rounded bead.

In still other embodiments of the invention, the spine stabilizationsystem has an elongate rod, a bone fastener having a securing elementand a rounded head, and a coupling element. The coupling element mayhave a lower clamp element disposed on a first end of said head proximalto said securing element, said lower clamp comprising a seating surfacecorresponding approximately to receive a portion of the rounded surfaceof said head. One embodiment further includes an upper clamp elementdisposed on a second end of said head distal to said securing element.In some cases, the lower clamp and upper clamp may have a projection anda notch that can interconnect to restrict rotation of one clamp withrespect to the other. Moreover, the system may also have a lockingelement disposed substantially around said first and second clampelements. The locking element also may further have an interior surfacethat is at least partially threaded. In some embodiments, the threadedportion of said locking element may be selectively engaged with saidthreaded portion of said lower clamp. These embodiments may also have arod locking element in communication with the upper clamp and lockingelement. Preferably, the rod locking element comprises a seating surfacefor receiving said elongate rod. As discussed above, a locking cap maybe selectively engaged with said rod locking element to secure saidelongate rod to said coupling element.

In still yet another embodiment of the present invention, the system mayhave a bone fastener having a rounded head and a coupling element. Inthis embodiment, the first end of the coupling element may have a skirtdisposed over said rounded head, wherein said skirt comprises a slitextending from a portion of the skirt proximal to the bone fastenertoward a distal end of said skirt, and wherein each of said distal andproximal ends of said skirt has one or more stops. The coupling ring maybe disposed over said distal end of said skirt, wherein said couplingring comprises one or more arms extending from said coupling ring to theproximal end of said skirt, and wherein said arms may be selectivelyengaged with said stops to lock said coupling element to said head. Onceagain, a locking cap may be selectively engaged with said couplingelement to lock said elongate rod to said coupling element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of the invention having an elongatedrod and a variable angle fastener with a wedge ring, a slotted bodydisposed around the head of a screw, and a locking cap;

FIG. 2 shows an isometric view of one embodiment of a wedge ring of theembodiment of FIG. 1;

FIG. 3 illustrates one embodiment of a variable angle fastener having a2-piece body, a wedge ring, and a locking cap;

FIG. 4 shows a top view of the variable angle fastener of FIG. 3;

FIG. 5 illustrates a variation of the embodiment of FIG. 3 using a1-piece body;

FIGS. 6A-6E illustrate different views of different coupling bodyembodiments of the present invention;

FIG. 7 is an isometric view of the 1-piece body of the embodiment ofFIG. 5;

FIG. 8 is a top view of the 1-piece body of the embodiment of FIG. 5;

FIG. 9 is a partial cross-sectional view of another embodiment of avariable angle fastener;

FIGS. 10-12 are additional illustrations of the variable angle fastenerof FIG. 9;

FIG. 13 illustrates another embodiment of the invention having a screw,a body, a locking ring slidably engaged with the body, and an optionalcap;

FIG. 14 illustrates an isometric view of the embodiment of FIG. 13;

FIG. 15 illustrates another embodiment of the invention having afastener with a flexible head configured to receive an elongated rod;

FIG. 16 illustrates a variation of the embodiment of FIG. 15;

FIG. 17 illustrates an isometric view of another embodiment of thepresent invention prior to assembly;

FIG. 18 illustrates an isometric view of the embodiment of FIG. 17 whenassembled;

FIG. 19 illustrates an isometric view of a cap of the embodiment of FIG.17;

FIG. 20 is an exploded side view of one embodiment of the presentinvention;

FIG. 21 is an exploded isometric view of the embodiment of the presentinvention of FIG. 20;

FIG. 22 is a closer exploded isometric view of a portion of theinvention of FIG. 17;

FIG. 23 is a closer exploded side view of a portion of the invention ofFIG. 17;

FIG. 24 is an assembled view of a portion of the invention of FIG. 17;

FIG. 25 is an isometric view of a skirt of the present invention of FIG.17;

FIG. 26 illustrates an isometric view of another embodiment of thepresent invention;

FIG. 27 is an cross section view of the assembled embodiment of FIG. 26;

FIG. 28 is a side view of the assembled embodiment of FIG. 26;

FIG. 29 is an exploded cross sectional view of the embodiment of FIG.26;

FIG. 30 is a partial cross sectional view of an embodiment of thepresent invention;

FIG. 31 is a cross sectional top view of an embodiment of the presentinvention;

FIG. 32 is a cross sectional top view of an embodiment of the presentinvention;

FIG. 33 is a cross sectional top view of an embodiment of the presentinvention;

FIG. 34 is a partial cross sectional view of an embodiment of thepresent invention;

FIG. 35 is a partial cross sectional top view of an embodiment of thepresent invention;

FIG. 36 is a partially exploded view of another embodiment of thepresent invention;

FIG. 37 is an alternate partially exploded view of FIG. 36;

FIG. 38 is a partial perspective (global) view of a cap of theembodiment of FIG. 36;

FIG. 39 is a side view of the embodiment of FIG. 36;

FIG. 40 is a partial perspective view of the embodiment of the FIG. 36;

FIG. 41 is a partially exploded perspective view of another embodimentof the present invention;

FIG. 42 is an perspective view of a cap of the embodiment of the FIG.41;

FIG. 43 is a cross-sectional view of the cap of FIG. 42;

FIG. 44 is a cross-sectional view of a coupling body of the embodimentof FIG. 41;

FIG. 45 is a partial perspective view of the embodiment of FIG. 41 withthe cap shown in a first position;

FIG. 46 is a partial perspective view of the embodiment of FIG. 41 withthe cap shown in a second position;

FIG. 47 is a partially exploded view of another embodiment of thepresent invention;

FIG. 48 perspective view of a cap of the embodiment of FIG. 47;

FIG. 49 is a cross-sectional view of the cap of the embodiment of FIG.47;

FIG. 50 is perspective view of the coupling body of the embodiment ofFIG. 47;

FIG. 51 is a cross sectional view of the embodiment of FIG. 47;

FIG. 52 is a partial perspective view of the embodiment of FIG. 47;

FIG. 53 is a partial perspective view of the embodiment of FIG. 47;

FIG. 54 is a perspective view of another embodiment of the presentinvention;

FIG. 55 is a partially exploded view of the embodiment of FIG. 54;

FIG. 56 is a perspective view of the embodiment of FIG. 54;

FIG. 57 is an partially exploded perspective view of the cap andcoupling body of the embodiment of FIG. 54;

FIG. 58 is a cross sectional view of the cap and coupling body of theembodiment of FIG. 54 with the cap shown in a first position;

FIG. 59 is a cross sectional view of the cap and coupling body of theembodiment of FIG. 54 with the cap shown in a second position;

FIG. 60 is a partially exploded view of the embodiment of FIG. 54; and

FIG. 61 is a partially exploded view of the cap and set screw of theembodiment of FIG. 54.

FIG. 62 is a perspective view of a coupling body of another embodimentof the present invention.

FIG. 63 is a perspective view of a coupling body of another embodimentof the present invention.

FIG. 64 is a perspective view of a coupling body of another embodimentof the present invention.

FIG. 65 is a perspective view of a coupling body of another embodimentof the present invention.

FIG. 66 is a perspective view of a coupling body of another embodimentof the present invention.

FIG. 67 is a perspective view of a coupling body of another embodimentof the present invention.

FIG. 68 is a perspective view of a coupling body of another embodimentof the present invention.

FIG. 69 is a perspective view of another embodiment of the presentinvention with the cap in a first position.

FIG. 70 is a perspective view of another embodiment of the presentinvention with the cap in a second position.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally is directed toward a spinal fixationsystem whereby the locking of an elongate rod plays may not be necessaryin order to lock the angle between a fastener, such as a screw, and acoupling element. Instead of requiring full application of lockingpressure on an elongated rod in order to lock the coupling elementsecurely in place with respect to the screw head, some embodiments ofthe present invention utilize a coupling locking device that is capableof securing the coupling element to the screw independent of the rod orwith forces imparted by the rod that are less than the forces used tolock the rod in place. Likewise, some embodiments of the presentinvention also may utilize a rod locking device that is capable ofsecuring the rod to the coupling element in a manner that is independentof the coupling locking device. In addition, some embodiments of thepresent invention permit a coupling element to lock in place relative tothe fastener head by downward movement of the elongated rod. Once thecoupling element is locked, the rod may be moved upward or repositionedwithout causing the coupling element to unlock or come loose. Thus,unlike prior spine stabilization systems, many embodiments of thepresent invention permit separately locking or unlocking of either therod and coupling element or the coupling element and screw.

As explained by the examples and illustrations below, the couplinglocking device and the rod locking device can be configured and adaptedin several different ways while still allowing independent operation orindependent locking. Through the means of cams, wedges, or threads, thisinvention can place a compression on the head of the screw without useof the elongated rod. The invention further seeks to reduce the numberof steps in the procedure, reduce the size of the coupling element, andreduce the number of separate pieces associated with the implant. Thiswill reduce intra operative time, create less complicated procedures,and work well in a wider variety of patient anatomy.

While many features of the invention will be described more fully belowwith reference to the accompanying drawings illustrating severalembodiments of the invention, it is to be understood at the outset thatskilled artisans having the benefit of this disclosure may recognizefurther variations or modifications of the invention that may alsoachieve the functions and results of this invention. Accordingly, thedescriptions which follow are to be understood as illustrative andexemplary of specific structures, aspects, and features within the broadscope of the invention and not as limiting of such broad scope.

Each of the embodiments described below and in the associated figuresdescribes a polyaxial fastener having a screw and coupling elementassembly for use with an orthopedic rod implantation apparatus. Whilethe embodiments are described and illustrated as having a screw that hasa head and a shaft that extends from the head, it should be understoodthat other fasteners or securing elements may also be used such as, forexample, lamina hooks and sacral blocks. Thus, the present invention maybe used with a wide variety of fasteners or securing elements inaddition to a bone screw as described herein.

Accordingly, FIG. 1 illustrates a side view of a screw 20 suitable foruse in the invention. The screw 20 includes a head 22 and a shaft 24that extends from the head 22. The shaft 24 is shown as having a taperedshape, which may be configured with a high pitch thread, although onceagain, skilled artisans would recognize that other shaft designs alsowould be compatible with the invention. Thus, the physician is free toselect from a variety of shaft features, such as thread pitch, shaftdiameter to thread diameter ratio, overall shaft shape, and the likeaccording to the conditions of the individual patient's bone.

While the head 22 may have any shape, it is preferred that the head hasa tapered neck with a rounded head to provide increased adjustability.Thus, at least a portion of the head may be shaped to form a portion ofa ball or at least a portion of a sphere above the neck in order toallow for rotational or angular adjustment of the coupling element 26with respect to the fastener 20. This preferred configuration alsoallows the coupling element 26 to more securely grip the head 22. Inother words, at least a portion of the head 22 has a curved surface fromwhich the shaft extends. The curved portion of the head can be asemi-spherical in shape, exhibiting an external contour that isequidistant from a center point of the head. In addition, the head mayhave an engagement surface that can be engaged by a screwdriving tool orother device, it is preferable that the engagement surface does notdisrupt the functionality of the curved surface.

The diameter of the head 22 may be approximately the same as the largestdiameter of the shaft 24. The neck may be tapered to provide greatercurvature of the head 22 in order to provide a greater variety of anglesand positions in which the coupling body and screw or fastener may bearranged. It should be noted that in other embodiments, the diameter ofthe shaft 24 can be less than or greater than the diameter of the head22, and the neck may be un-tapered or differently tapered.

The head 22 also may have an engagement surface that permits thephysician to apply torsional or axial forces to the screw with a wrenchor screwdriving tool to drive the screw into the bone. For instance, theengagement surface of the head 22 may be a polygonal recess as shown inFIG. 10 in which the head of a tool can engage. For example, the head 22may have a hexagonal recess that receives a hexagonal tool such as anallen wrench. The engagement surface also may be configured with aprotruding engagement surface that likewise may engage with a tool ordevice having a corresponding recess, although preferably the protrudingengagement surface would not significantly interfere with the capabilityto vary the angle of the coupling element with respect to the screw 20.The engagement surface may have other shapes as well, such as a slot ora cross found typically used with other types of screwdrivers.

Prior to being locked into place, a coupling element 26 associated withthe head 26 can be moved and rotated into a plurality of positions. Thecoupling element is configured and adapted with a seat or interiorsurface that receives the head 22 on a first end and an elongated rod onthe opposing end. At least a portion of the head may have a roughened ortextured surface that improvise engagement between it and othercomponent of the polyaxial screw when in a locked or tightened position.With respect to the embodiment shown in FIG. 1, the coupling elementcomprises a coupling ring 28 and a coupling body 30. The coupling bodyhas a skirt 32 that defines the seat or interior surface that receivesthe head 22. Preferably, the skirt may be selectively locked or unlockedagainst the head by providing one or more slits or openings that allowthe seat or interior surface of the coupling element to constrict andsecurely engage with the head 22 in a locked position or be expanded orunlocked as desired. In one embodiment, shown in FIG. 1, the couplingbody has one or more generally helical slits. More preferably, the slitsor openings extend from a free end of the skirt proximate to the screwor fastener 20 to a location above the head 22.

The coupling body 30 has a plurality of stops 34, preferably disposednear the upper and lower ends of the coupling body skirt 32. The stops34 may be configured with flanges with openings or slots through whichthe coupling ring may be placed so that the skirt 32 approximates theshape of a spool. The stops 34 are positioned so that as the couplingring 28 is connected to the coupling body 30 torsional forces areapplied to the skirt 32 causing it to twist and constrict against thehead 22.

As shown in FIG. 1, the coupling ring 28 is configured to have one, two,or more arms 36 that extend from the ring 28 and engage with the stops34. As the coupling ring 28 is placed onto the coupling body 30, thearms 36 slidably engage with the stops with minimal torsional forcesimparted to the skirt until a wedge near the base of the arms proximalto the ring contacts one of the stops. After the wedge has engaged withone of the stops, further insertion of the ring over the coupling bodywill cause it to turn about the longitudinal axis of the skirt. As thering is turned, the distal end of the arms will engage with stops 34 andapply torsional forces to the skirt. In one embodiment, the locking ringrotates from about 2° to about 15° from its initial, unlocked positionuntil reaching a locked position where the coupling element is immovablysecured to the screw. In another embodiment, the locking ring rotatesfrom about 5° to about 10° from an unlocked to a locked position.

Preferably, the distal end of the ring arms 36 are configured toradially engage with a lip on the skirt once the skirt has beensufficiently turned to lock against the screw head 22. As shown in FIG.2, for example, the distal end of the ring arm may have protrusions 38that extend radially inward. The protrusions 38 can slide over the lipof the skirt and snap into place once the skirt is in its lockedposition. Initially, when the skirt is not in a locked position, thelength of the ring arms L_(ra) from the proximal end to the protrusionmay be less than the length of the skirt L_(s). As the skirt is twisted,however, its overall length may gradually decrease, and the ring armswill splay outward as the protrusions are forced over the lip. Once thelength of the skirt L_(s), becomes approximately the same length, orshorter than the length of the ring arms L_(ra), the protrusions will bereleased over the lip and hold the skirt in its locked position. In thisembodiment, unlocking the coupling body skirt 32 from the screw head 22can be accomplished by applying a radially outward force to the ringarms until the protrusions no longer engage with the lip. Once theprotrusions are clear of the lip, the coupling ring may be rotated tounlock the coupling element. In this manner, the coupling element may beselectively locked or unlocked to the screw or fastener 20 withoutrequiring the elongated rod to be locked in position. Thus, no forcesneed be imparted by the elongated rod to lock the coupling element tothe screw or fastener.

Returning to FIG. 1, the coupling body also is configured and adapted toreceive an elongated rod on an upper end opposite the end of thecoupling body 30 configured with the coupling body skirt 32. Preferably,this portion of the coupling body is configured with a U-shaped or wedgeshaped seat against which the elongate rod will be locked. Substantiallyrigid tines or wedges extend upward from the seat for the rod, which areconfigured with slots or detents that receive a cap 40. The cap, such asillustrated in FIGS. 3 and 17, may have corresponding protrusions orslots that permit the cap to engage with and rotate with respect to thecoupling body 30. In one embodiment, rotation of the cap causes it tomove downward and toward the screw, thereby applying a downward forceagainst the elongate rod to hold it securely in place.

In another embodiment, the cap applies a downward pressure on theelongate rod that, in turn, causes the coupling element to be locked inposition relative to the fastener while not completely locking theelongate rod in position. A set screw disposed in the cap may then applyadditional downward pressure on the elongate rod to hold it firmly inposition. Thus, in some embodiments the downward pressure of the cap onthe rod may be sufficient to lock one component of the system whilestill allowing adjustability of the other component.

In an another alternative embodiment, the tines or wedges of thecoupling body that extend upward from the seat for the rod may beflexible so that they bend or flex around the rod as the cap is turnedtoward a locking position. For instance, either the cap, the tines orwedges, or both may be configured to have a tapered or ramped surfacethat causes gradually increasing radial interference with the cap andcoupling element as the cap is rotated. As the radial forces resultingfrom this interference increases, the tines or wedges may bend or flexradially inward and press against the elongate rod. One or more detentsand depressions may be placed on either the cap or the coupling body tohold the cap in a locked position by engaging with each other at adesired cap position. Rotation of the cap in the opposite directionlikewise causes the elongated rod to become unlocked.

Thus, in several embodiments of the invention the elongate rod may beselectively locked or unlocked in place without requiring the couplingbody to be unlocked from its position with respect to the screw.

FIGS. 3-8 illustrate several features and variations of yet anotherembodiment of the invention. Several features of this embodiment aresimilar to those described above. For example, the screw or fastener 20may be configured or varied according to the physician's preference. Ithas a head 22 on-which a coupling element 26 communicates. As mentionedabove, the head 22 may be generally spherical in shape. The couplingelement 26 may be positioned and rotated in several directions, and maybe selectively locked or unlocked in position. The coupling elementlikewise has a coupling body 30 and coupling ring 28 with ring arms 36that is capable of locking the coupling element 26 to the screw orfastener 20.

Rather than using a skirt that twists or rotates to lock the couplingelement to the screw or fastener, however, the coupling body of thisembodiment may be formed of one, two, or more coupling body components42 that are configured with at least two stops that slidably engage withat least one ring arm 36. As shown in FIG. 5, the coupling body has atleast one slit or opening extending substantially along the length ofthe coupling body component. More preferably, at least one slit oropening extends entirely along the length of the coupling bodycomponent, as shown for example in FIGS. 5 and 7. In one embodiment, thenumber of slits or opening configured in this manner increases as thenumber of coupling body components 42 increases. Thus, a coupling body30 comprising at least two coupling body components 42 also will have atleast two slits or openings extending generally along the axial lengthof the coupling body components.

The slit or opening is thus defined by corresponding terminating edgesof material formed on or more coupling body components 42. As shown inFIGS. 5 and 7, the shape of the slit or opening may be configured suchthat a portion of a first terminating edge may protrude into a recessedarea of a corresponding portion of a second terminating edge. Asmentioned previously, at least two stops 34 are configured to slidablyengage with at least one ring arm 36. These stops are positioned so thatas the tapered portions of the ring arms contact one or more of thestops the terminating edges defining the slit or opening are forcedtoward each other so that the coupling element can be locked to the headof the screw or fastener. This is accomplished by placing at least onestop on each side of the terminating edges defining the slit or opening.Thus, each ring arm may communicate with two or more stops. Morepreferably, at least three stops are configured to contact at least onering arm in order to close the coupling body onto the head 22. Thus, oneedge of the slit or opening may have two or more stops, while the othermay have one or more stops. Even more preferably, each ring arm isconfigured to communicate with at least three stops arranged in thismanner.

As shown in FIGS. 3, 5, and 6A, the terminating edges or the couplingbody components 42 may be configured in a tongue and groove fashion sothat the tapered surface of the ring arm contacts the stops on thetrailing edge of the stop rather than at the leading edge. It is notnecessary, however, that the terminating edges have this configuration.FIGS. 6B-D, for instance, illustrate some variations of this embodimentthat do not utilize a tongue and groove configuration. Moreparticularly, FIG. 6B illustrates that multiple wedges may be providedon the ring arms 36. This allows stops to be placed in differentlocations along the axial length of the coupling body, such as to allowthe application of different amounts of gripping force on differentportions of head 22.

FIG. 6C shows that the stops may be angled in a manner that helpsencourage the terminating edges closer together as the ring arms 36 aremoved toward a locking position. For instance, the angle of the stopsmay be from about 3° to about 15° off from the longitudinal axis of thecoupling element 26, and more preferably the stops may be angled fromabout 5° to about 100.

The embodiment of FIG. 6D uses a plurality of slits or openings thatgenerally are perpendicular to the longitudinal axis of the couplingelement 26. These slits or openings create an appearance of generallyhorizontal bands. Stops disposed near free ends of one or morehorizontal bands may slidingly engage with the ring arms as they aremoved toward a locking position, thereby causing the terminatingsurfaces of the horizontal bands to move toward each other to grip thehead 22.

Locking mechanisms may be used in any of the embodiments describedherein to hold the ring arms onto the coupling body in a lockedposition. As mentioned above, many different types of forces, such astorsional loading around or axial loading along the longitudinal axis ofthe coupling element 26, may be applied to the coupling ring 28 and ringarms 36 in order to lock the coupling element in position. Theembodiments shown in FIGS. 6A-D, for example, have locking mechanismsdisposed on the free ends of one or more ring arms.

The coupling element 26 may have a seat for receiving an elongated rod,and further may have tines that engage with a cap to independently lockthe coupling element to an elongated rod. In some embodiments, thecoupling element may be securely positioned with respect to the fastenerhead with little or no additional pressure applied to the head 22. Forexample, the cap may provide pressure to the sides of the tines on thecoupling element, which in turn flex or bend to securely grip theelongated rod.

FIGS. 9-12 illustrate an embodiment of the invention that does notutilize a coupling ring with ring arms applying forces to stops in orderto cause the coupling element to flex or bend around the head 22.Instead, this embodiment uses a multiple piece threaded lock to clampthe coupling element to the fastener 20. For example, FIG. 9 illustratesa coupling element formed from a lower clamp element 44, an upper clampelement 46, a threaded locking nut 48, and an elongated rod locking nut50.

FIG. 11 illustrates the assembly of the polyaxial screw of thisembodiment of the invention. During assembly, the upper clamp element46, elongated rod locking nut 50, and threaded locking nut 48 arepositioned over the head 22 of the fastener 20 that is distal to thescrew shaft 24. The lower clamp element 44 then is placed onto the head22 by passing the screw head through its open center. The lower clampelement 44 preferably has threads that engage with the threads of thethreaded locking nut 48. As these threads are increasingly engaged, theupper and lower clamp elements 44 and 46 gradually clamp onto the head22 until the coupling element is securely in place.

FIG. 9 shows that the interface between the upper and lower clampelements may be engaged in a manner that prevents rotation of the clampelements as the threaded locking nut is turned. In one embodiment, theupper and lower clamp elements utilize corresponding square toothpatterns on the clamping elements. Other patterns also may be used forthe interconnecting surfaces, such as a sawtooth, a ratchet, or thelike. The edges also may have roughened surfaces, such as a star grind,to help prevent rotation of the clamp elements, although it is morepreferred that the interlocking surfaces of larger dimensions be used inorder to ensure that the surfaces interconnect and resist rotation.

The elongated rod may be locked in place by turning the elongated rodlocking washer or nut so that the tines of the coupling element flex orbend to grip the rod. As shown in FIG. 9, the tines may be formed on theupper clamp. In this embodiment a cap as previously described forlocking the elongated rod in place may or may not be present. Forexample, the elongated rod locking washer may have one or more cams onits internal surface that urges the tines to bend or flex tightly aroundthe elongated rod when the washer is turned or rotated. Preferably,turning the washer from about 5° to about 25° causes the elongated rodto be either locked or unlocked. More preferably, the washer can beturned from about 10° to about 25°. If desired, a cap may be provided tofurther ensure that the rod is securely held in place. A set screw mayalso be provided in the cap to apply additional locking forces to theelongated rod.

FIGS. 13 and 14 illustrate another embodiment of the invention that onceagain uses a coupling body skirt with slots or openings formed therein.In this embodiment, the coupling body skirt may be angled by from about5° to about 30°, and more preferably is from about 7° to about 15°.While the figures illustrate that the taper of the coupling elementgradually expands the diameter of the tapered portion of the couplingbody skirt 32 from the end proximate the screw shaft 24 to the upper endnear the elongated rod, skilled artisans would appreciate that the tapercould be inverted.

A locking ring 52 disposed around the coupling body skirt is capable ofcausing the coupling element to clamp securely to the fastener 20 simplyby moving it in an axial direction along a tapered surface of thecoupling body skirt 32. One advantage of this embodiment over theembodiments of FIGS. 9-11 is that there is no need to apply a wrench toa threaded locking nut. Additionally, in this embodiment the couplingbody may be formed from only two elements instead of four. Thus, thisembodiment may be advantageous over other embodiments at least for itsimplicity of operation and design.

In operation, once the coupling element is in a desired position, thelocking ring 52 may be moved vertically along the axis of the couplingbody skirt. As the ring is moved, it engages with and compresses thetapered region of the skirt, which in turn causes the skirt to flex andbend toward the head 22. Although not shown, a second ring may beprovided on the skirt to help independently lock the elongated rod tothe coupling body. This can be accomplished, for instance, by providingtines that reach above the elongated rod after the rod has beenpositioned within a seat of the coupling element.

In much the same manner as described above for locking the couplingelement 26 to the fastener 20, the second locking ring can be movedalong the axis of a second tapered coupling body skirt that isconfigured and adapted for locking the elongated rod. It may beadvantageous to configure the first and second tapered skirts andlocking rings so that the direction of movement for moving one lockingring into a locked position would cause the second locking ring to moveinto an unlocked position if moved in the same direction. In otherwords, for this embodiment it may be advantageous to configure thecoupling element so that locking of all components of the polyaxialscrew is effected by either moving the locking rings far apart or bymoving them toward each other.

Another alternative for locking the elongated rod is to use a cap 40.Any cap design for locking an elongated rod, including those alreadydescribed herein, may be used to securely connect the elongated rod withthe coupling element.

In general, the embodiments described above may be used to establish asubstantially rigid, immobilization of at least a portion of the spine.In some cases, however, it may be advantageous to use a system thatallows for some flexible support for at least a portion of the spine.The embodiment illustrated in FIGS. 15 an 16 describe one aspect of theinvention where the fastener 20 is capable of flexing or bending evenafter the components have been secured together. Although not requiredin order to practice the invention, in a preferred embodiment, thefastener and coupling element may be integrally formed.

The coupling element may have one or more slits or openings that providelimited range of flexibility. For instance, the coupling elements may beconfigured to permit from about 2° to about 7° of flex. To provide thisflexibility, the coupling element may be formed from one or more slitsor openings formed in its surface. In one embodiment, the slits oropenings in the coupling element are generally helical in shape. Otherflexible constructions also may be used. For instance, U.S. patentapplication Ser. No. 10/443,755, filed May 23, 2003, and which isincorporated herein in its entirety, provides several methods andconstructions for a flexible coupling element that may be used in thepresent invention. In addition, U.S. patent application Ser. No.10/762,533, filed Jan. 23, 2004 and which is also incorporated byreference in its entirety, provides additional methods and constructionsthat may be used with the present invention.

A seat for receiving the elongated rod may also be integrally formedinto the fastener, although once again such a construction is notrequired in order to practice the invention. The seat may be formed froma plurality of tines in the manner previously described, oralternatively may have a threaded surface in which a locking cap 54 isplaced over the rod. As the locking cap is turned, its lower surfacepresses against the upper surface of the elongated rod until the rod issecurely held in place.

FIGS. 17-19 illustrate another embodiment of the invention using amultiple piece threaded locking nut to clamp the coupling element 26 tothe fastener 20. As shown in FIG. 17, the coupling element 26 comprisesa lower clamp element 44, an upper clamp element 46, a threaded lockingnut 48. The upper and lower clamp elements 44 and 46 haveinterconnecting edges that, when joined, help prevent rotation of oneclamp element with respect to the other. As shown in FIG. 17, forexample, the interconnected edges of the upper and lower clamp elements44 and 46 may have an interconnecting pattern of teeth. Skilled artisanswould recognize that other interconnecting edge patterns also may beused to help prevent rotation of the clamp elements with respect to eachother.

A portion of the lower clamp element 44 is threaded on its outer surfacein order to receive corresponding threads on the inner surface of thethreaded locking nut 48. Tightening of the threaded locking nut 48causes the upper and lower clamp elements 44 and 46 to move towards eachother in order to lock the coupling body 30 onto the head 22.

The upper and lower clamp elements 44 and 46 have seating surfaces thatconform to a portion of the curved surface of the fastener head 22.Preferably, the radius of curvature of the rounded or semi-sphericalportion of the head 22 is the substantially the same as the radius ofcurvature for the seating surfaces of the upper and lower clampelements. Once the clamp elements have fully contacted the head 22,however, a gap or opening may remain between the upper most or lowermost regions of the interconnecting edges. For instance, the spacebetween the uppermost edge of an upwardly extending square tongue of thelower clamping element 44 and the uppermost edge of a correspondingsquare groove of the upper clamping element 46 may be from about 1 mm toabout 5 mm in height.

While the upper clamp element 46 has a lower edge that interconnectswith the edge of the lower clamp, it also has an upper edge on thedistal end from the interconnecting edge that engages with otherelements of the coupling body to form a seat that receives the elongatedrod. In particular, the distal end of the upper clamp element 46 extendsabove the threaded locking nut 48 and through an aperture formed in arod seating and locking element 58 disposed above the threaded lockingnut 48. The rod seating and locking element 58 has a curved seatingsurface that receives the elongated rod, but also is configured with arecess 60 to receive the distal end of the upper clamp element 46.

In particular, the distal end of the upper clamp 46 has two or morewings 56 that extend radially outward from the distal end of the clamp.As shown in FIG. 17, the threaded locking nut 48 and rod seating andlocking element 58 are notched to permit the wings 56 to pass throughthem when the wings are aligned with the notches. Once the wings aredisposed above the seating surface of the rod seating and lockingelement 58, either the upper clamp 46 or the locking element 58 may berotated until the recess 60 is aligned with the wings 56. The wings 56are then placed within the recess 60 to form the seating surface onwhich the elongated rod will be placed.

Once the elongated rod is positioned over the seating surface of thelocking element 58 and the wings 56 of the upper clamping element 46, alocking cap 62 may be joined with the locking element 58 to securelyconnect the coupling element 26 to the rod. The manner in which the cap62 and locking element 58 apply a locking force on the elongated rod mayvary. In one embodiment, the locking cap is configured to apply adownward force on the elongated rod as it is joined with the lockingelement 58. As shown in FIG. 17, the locking element 58 may have one ormore tabs that engage with the cap 62 to move the cap downward upon therod.

Referring to FIG. 19, the cap may have a curved ridge or tooth 66extending along a portion of the circumference of the cap on itsinterior surface. The length of the curved ridge 66 may be determined inpart upon the amount or rotation the cap will undergo when moving froman unlocked position to a locked position over the elongated rod. Forinstance, one or more curved ridges may extend from about 3° to about30° of the cap, and more preferably extends from about 10° to about 20°.The curved ridge 66 engages with the underside of the tab 64.

Either the curved ridge 66, the tab 64, or both may be configured tocreate a cammed surface that forces the cap downward as it is rotatedtoward a locked position. The tab and ridge also may be configured withone or more detents and recesses that are capable of providing a tactileor audible signal to the physician, such as click that may-be felt orheard, of when the cap has reached its locked position. The detents andrecesses also may assist in maintaining the cap in its locked position.

Referring to FIG. 17, in a preferred embodiment the locking element 58has an outer surface 68 below the tabs 64 that is generally cylindricalin shape. The cap 62 likewise has a corresponding generally cylindricalsurface 70 of similar diameter. When the cap is placed over the lockingelement, these two surfaces may help maintain radial positioning of thecap 62 relative to the locking element 58 as the cap is turned toward alocking position.

In one alternative embodiment, the locking element 58 and cap 62 may beconfigured compress a portion of the seating surface around the rod tolock it in place in a manner similar to FIGS. 9 and 14. Thus, thisalternative embodiment may involve modifying the generally cylindricalsurfaces 68 and 70 to create a cammed surface that applied radiallyinward forces upon a portion of the locking element. As the cap 62 isrotated toward a locking position, the radial forces increase and causea portion of the locking element 58 to flex, bend, and compress theelongate rod.

As shown in FIGS. 17-19, the cap of this embodiment may have a sidewall72 that extends from the top of the cap 62 toward the screw shaft 24.Preferably the cap sidewall 72 terminates near a lip or base of thelocking element 58, and both elements are configured to haveapproximately the same outer diameter. In order to place the cap overthe elongated rod the sidewalls 72 may have cutouts or notches 74 thatpermit the rod to extend through the sidewall 72 when the cap is placedover the locking element 58 in either a locked or unlocked position.Thus, the length of the cutouts or notches generally correspond to theamount of rotation needed to move the cap into or out of a lockedposition. The cutouts 74 also may be slightly larger than needed torotate the cap 62 in order to allow for possible tolerances in thedesign of the cap 62, the locking element 58, and the rod. For instance,the cutouts 74 may permit from about 1° to about 5° of additionalrotation than needed to lock or unlock the cap 62.

Several of the features or elements of the various embodiments describedherein may be modified and/or used with other embodiments withoutdeparting from the spirit and scope of the invention. FIGS. 20-25illustrate yet another embodiment of the invention that uses severalfeatures or elements described above. FIGS. 20-24 show how thecomponents of this embodiment may be configured, arranged, andassembled. As shown in FIG. 21, for instance, the coupling element 26may be formed of a coupling body and coupling ring. The coupling bodymay have one, two, or more coupling body components with at lest one,preferably two, slits or openings extending substantially, if notcompletely, along the axial length of the coupling body. The slits oropenings need not be straight, but rather may be defined by theterminating edges of material on the coupling body components 42. FIGS.20, 23 and 24 illustrate that the terminating edges of the coupling bodycomponents may be configured with a tongue and groove configuration.Likewise, a single coupling body component such as shown in FIGS. 7 and8 may be used in place of a plurality of coupling body components.

Likewise, one terminating edge may define a first substantiallyhorizontal protrusion disposed above a second substantially horizontalprotrusion defined by the opposing terminating edge so that the firstand second protrusions are substantially layered or sandwiched together.Stops may be disposed on the coupling body components near each slit. Atleast one stop may be provided on opposite sides of the slit or opening.Thus, where the illustrated example uses two coupling body components,there are at least two stops on both components. The coupling bodycomponents may be disposed around the rounded fastener head.Subsequently, a ring may be pressed or lowered downward over thecoupling body components. As the ring is lowered, one or more armsslidingly engage with the stops. Further downward movement of the ringand arms may then cause the coupling body components to securely gripthe fastener head. FIG. 24 illustrates that the arm may define a wedgeshape that pushes the stops on the coupling body components furtherapart from each other, which in turn causes the components to applygreater gripping force upon the fastener head.

Skilled artisans would appreciate, however, that other configurations ofstops may also be used to securely grip the fastener head, including anyof the other configurations previously described above. For instance,the configurations illustrated in FIGS. 1 and 6B-E may also be utilizedto push the stops closer together in order to increase the grippingforces applied to the fastener head.

Turning to FIG. 24, the coupling body components may be configured tojoin together to grip the screw head. In this embodiment, a firstcoupling body component may have two prongs or arms on each side thatextend outward to define a recess therebetween. The second coupling bodycomponent may then be configured with one arm on each side thatcorresponds generally to the recesses formed in the first component.

The interior surfaces of the coupling body components may be roughenedor textured to more securely grip the screw head. As shown, the interiorsurfaces may be textured with a plurality of grooves or circular cuts.The interior surfaces of both components may have similar texturedformed thereon, or alternatively may have different textures or textureorientations. For instance, the grooves or circular cuts on one interiorsurface may be oriented in one direction, such as being directedgenerally horizontally, while grooves or cuts on a second interiorsurface may be oriented in a different direction, such as vertically, sothat the angle formed between the direction of the grooves or cuts ofthe first surface and the direction of the grooves or cuts of the secondsurface is from about 60° to about 90°. In one embodiment, the grippingpressure applied to the fastener head causes the raised portions of thesurfaces having grooves to deform or cut into an opposing groovedsurface, thereby further resisting unintended movement or repositioningof the components. Additionally, helical grooves may be provided oneither a portion of the fastener head, on a gripping surface of one ormore coupling elements, or both.

Once the coupling body component are place around the screw head, ringarm 36 may be place over the coupling element so that downward extendingarms of the ring arm begin to engage with the stops to hold the couplingbody components onto the screw head. In addition, the coupling bodycomponents and screw head may be lowered into the skirt. Turning to FIG.25, the lower portion of the skirt may have a lip or retaining ring thatis capable of supporting the fastener and assembled components disposedaround its head. The lip may be a unitary surface extending inwardaround the entirety of the perimeter of the lower portion of the skirt,or alternatively may be formed of a plurality of tabs or protrusionsthat cooperate to prevent the assembled components from passing throughthe lower end of the skirt. The portion of the fastener head andassembly that rests against the lip may be shaped or configured todistribute the axial loading placed on the lip in substantially equalportions. In one embodiment, the surface of the lip that contacts theassembly is substantially flat and resides in a plane that isperpendicular to the longitudinal axis of the skirt. The shape of thecontacting surface of the lip may have other shapes as well, such as afrustoconical shape, a partially spherical shape, a sawtooth or ridgedshape such as illustrated in FIG. 9, or the like.

Above the lip, the skirt has a recess formed therein where the assemblymay be placed. The ring arm may then be disposed over the assembly inthe manner described above. The ring arm is configured with a curvedseating surface on its upper side that is shaped to receive an elongaterod. The skirt also has two openings or slots on its upper side forreceiving the elongate rod.

As the rod is fitted through the opening or slots on the skirt andpressed on the ring arm seating surface, the ring arm may be urgedfurther down, thereby causing the coupling element to close further uponthe screw head. The forces applied on the screw head, however, may notyet fully prevent the skirt and assembly from being rotated, moved, oradjusted. A cap may then be lowered onto the skirt over the rod. Asshown in FIG. 25, the cap may have two enlarged openings or slots thatare wider than the opening of the skirt and wider than the diameter ofan elongated rod that may be placed in the skirt. This embodimentpermits the cap to be turned or rotated without the sidewalls of theopenings or slots from being obstructed by the rod. Preferably, theopenings or slots are configured to permit from about 5° to about 90° ofrotation of the cap, or alternatively permit from about 15° to about 60°of rotation of the cap. In yet another embodiment, the openings or slotsin the cap are configured to permit from about 20° to about 40° ofrotation of the cap without being obstructed by the rod.

When the cap is turned to a first position, it engages with the skirt toprevent its inadvertent removal. In this position, the rod may remainfree to be moved or slide through the openings of the skirt and cap, andthe skirt may still be adjusted or moved relative to the screw orfastener. As the cap is turned further to a second position, however, acam or inclined surface on the upper portion of the enlarged openings orslots may urge the rod further downward onto the ring arm, therebycausing the ring arm and coupling body components to securely grip thefastener head so that the skirt can no longer move relative to the screwor fastener. As mentioned above, the locking of the coupling bodycomponents in this manner may not also cause the cap to fully lock theelongated rod to the skirt. In fact, once the coupling body is lockedonto the fastener head, the cap may be loosened and the elongated rodrepositioned without inadvertently causing the coupling body to becomeunlocked from the fastener head.

Alternatively, the cap may be urged further down into the skirt as it isturned toward the second, locking position. As the cap is lowered, theupper portion of the enlarged opening or slot, which may or may not havea cam or incline, will press the rod against the seat of the ring arm.For instance, the cap and skirt may be configured with threads that drawthe cap into the skirt when it is turned in one direction and releasesthe cap from the skirt when turned in the opposite direction.

Preferably, the skirt and/or cap are configured to provide a tactilefeel or audible click when the cap reaches either the first or secondposition, or both positions. One advantage of this is that the physicianwill receive confirmation that the assembly is in a desired position. Inaddition, the cap and skirt may be configured with one or more detentsor similar mechanisms to help prevent the cap from inadvertently backingout of either the first or second positions.

While the skirt and fastener may be fixed in position relative to eachother once the cap is in the second position, the rod may still becapable of sliding through the openings of the skirt and cap. The capmay be configured with an aperture disposed on its upper surface where aset screw may be utilized to securely hold the rod in place once it isin its desired position.

FIGS. 26-29 illustrate yet another embodiment of the invention that usesseveral features or elements described above. FIGS. 26-29 show how thecomponents of this embodiment may be configured, arranged, andassembled. In this particular embodiment, a coupling element comprisedof coupling body components 1 10 and a coupling wedge 120 is used togrip the fastener 130.

As shown in FIG. 26, the coupling element may be formed of a couplingbody 140, coupling body components 110, and coupling wedge 120. In thisembodiment, the coupling body components 110 are capable of gripping ortightening around the fastener head as a result of any downward forceimparted upon the coupling wedge 120. The coupling body 140 is comprisedof a top and bottom portion, wherein the bottom portion comprises askirt or inner surface portion 150 of the coupling body that isconfigured to receive both the coupling body components 110 and couplingwedge 120. One advantage of this present embodiment is that the couplingelement is of a simple construction, is easy to install, and allows forthe precise placement and adjustment of the elongated rod in relation tothe inserted fastener.

As shown in FIG. 26, during assembly, the coupling body components 110are placed around the head of a fastener 130. The coupling wedge 120 isplaced above the coupling body components 110. The assembled parts maythen be inserted into the coupling body 140. As a downward force isapplied to the coupling wedge 120, the coupling wedge 120 interacts withthe coupling body components 110 and the inner surface portion 150 ofthe coupling body 140 to cause the coupling body components 110 totighten around the fastener head, locking the coupling element in placein relation to the fastener 130.

As shown in FIG. 26, the coupling element may have one, two, or morecoupling body components 110 with at least one, preferably two, slits oropenings extending substantially, if not completely, along the axiallength of the coupling body. As described previously, the slits oropenings need not be straight, but rather may be defined by theterminating edges of material on the coupling body components 110. Asopposed to previous embodiments however, the coupling body components110 of the present embodiment do not contain protrusions, stops, orother engagable material as described above. Rather, in this particularembodiment and as shown in FIG. 26 and FIG. 29, the coupling bodycomponents 110 are substantially cylindrical in shape and may bedesigned with a an upper surface 112 and lower surface 114 that istapered or of a truncated conical shape. The upper and lower surface112, 114 of the coupling body components 110 are designed to interactwith the coupling wedge 120 and inner surface portion 150 such that anydownward force applied to the coupling wedge 120, causes the couplingbody components 110 to tighten around the fastener head.

In one embodiment, the interior surfaces of the coupling body components110 may be roughened or textured to more securely grip the screw heads.As described previously, the interior surfaces may be textured with aplurality of grooves or circular cuts. The interior surfaces of thecomponents may have similar textured surfaces or alternatively may havedifferent textures or orientations of the textured surfaces. Forexample, in one embodiment the gripping pressure applied to the fastenerhead causes the raised portions of the surfaces having grooves to deformor cut into an opposing grooved surface, thereby further resistingunintended movement or repositioning of the components.

The coupling wedge 120 is substantially cylindrical and may contain anaperture providing access through the coupling wedge 120 to the top ofthe fastener head. As shown in FIG. 26 and FIG. 29, the coupling wedge120 is ring-like and is designed to engage the upper surface 112 of thecoupling body components 110. The bottom surface 122 of the couplingwedge 120 may cooperatively engage with the upper surface 112 of thecoupling body components 110. For example, the coupling wedge 120 of oneembodiment may be formed with a tapered bottom surface 122 or truncatedconical surface. As described previously, the upper surface 112 of thecoupling body components 110 has a tapered surface as well. Whenassembled, the bottom surface 122 of the coupling wedge 120 and theupper surface 112 of the coupling body components 110 interact such thatany downward force applied to the coupling wedge 120 causes the couplingbody components 110 to tighten around the fastener head. This grippingforce imparted to the fastener head results from the interaction of thecoupling wedge 120 and coupling body components 110. While in thisparticular embodiment the bottom surface 122 of the coupling wedge 120and upper surface 112 of the coupling body components 110 are describedas tapered or truncated conical surfaces, it will be apparent to one ofordinary skill in the art that surfaces of the interacting componentsmay be altered, modified, or changed so long as any downward force onthe coupling wedge 120 imparts a force to the coupling body components110 causing or urging the coupling body components 110 to tighten aroundor grip the fastener head.

Prior to imparting any downward force onto the coupling wedge 120, thecoupling body components 110 and coupling wedge 120 are placed aroundthe fastener head. This assembly is then lowered into the coupling body140. Turning to FIG. 29, the lower portion of the coupling body 140 iscomprised of a inner surface portion 150 that may have a lip 152 orretaining ring that is capable of supporting the fastener and assembledcomponents disposed around its head. As described previously, the lip152 may be a unitary surface extending inward around the entirety of theperimeter of the lower portion of the inner surface portion 150, oralternatively may be formed of a plurality of tabs or protrusions thatcooperate to prevent the assembled components from passing through thelower end of the inner surface portion 150. Additionally, the lowersurfaces 114 of the coupling body components may also be formed with atapered edge or truncated conical surface. The degree to which the edgeis tapered can vary but should be of a degree sufficient to prevent thecoupling body components and head of the fastener from slipping throughthe bottom of the inner surface portion when assembled. In thisembodiment, the lip 152 of the lower portion of the inner surfaceportion cooperatively engages the lower surface 114 of the coupling bodycomponents 110 such that when a downward force is applied to theassembled components, the interaction between the lower portion of theinner surface portion 150 and lower surfaces 114 of the coupling bodycomponents 110 causes the coupling body components 110 to tighten orgrip the fastener head. Even where the lip 152 of the inner surfaceportion 150 does not contain a surface designed to specifically matchthe lower surface 114 of the coupling body components 110, any downwardforce applied to the assembled components may still provide for thetranslation of force perpendicular to the applied downward force, whichin turn tightens or urges the coupling body components 110 to tightenaround a fastener head. In one embodiment, the lip of the inner surfaceportion may be an inwardly inclined surface from anywhere greater than1°. For example, in FIG. 28, the lower portion of the inner surfaceportion is in inwardly inclined surface. The incline is configured ordesigned so that the fastener head will not slip through the innersurface portion and coupling body component assembly.

When assembled, the interaction between the coupling wedge 120, innersurface portion lip 152, and coupling body components 110 results in thetightening of the coupling body components 110 around the fastener head.The coupling element when assembled and installed, creates asubstantially rigid structure in a fixed position, i.e., the couplingelement is locked to the fastener 130.

As described in previous embodiments and with reference to FIGS. 26, 27,and 29, the coupling body 140 is configured and adapted to receive anelongated rod 160 on an upper end opposite the end of the coupling bodyconfigured with the coupling body skirt 150. Preferably, this portion ofthe coupling body 140 is configured with a U-shaped or wedge shaped seatagainst which the elongate rod will be locked. Substantially rigid tinesor wedges extend upward from the seat for the rod, which are configuredwith slots or detents that receive a cap 170. The upper portion of thecoupling body 140 is also configured to permit the elongated rod 160 toexert force upon the coupling wedge 120. The coupling wedge 120 may beconfigured to receive the elongated rod 160 or may not. But in eithercase, the design of the upper portion of the coupling body 140 mustallow for the elongate rod 160 to exert a downward force upon thecoupling wedge 120 in order for the coupling wedge 120 to transmit thatforce to the coupling body components 1 10.

The cap 170, such as illustrated in FIG. 29, may have correspondingprotrusions or slots that permit the cap 170 to engage with and rotatewith respect to the coupling body 140. In one embodiment, rotation ofthe cap 170 causes it to move downward and toward the elongate rod 160,thereby applying a downward force against the elongate rod 160 to holdit securely in place. The downward force is transmitted through theelongate rod 160 to the coupling wedge 120, which in turn transmits theforce to the coupling body components 1 10. As a result of this design,the coupling element and elongate rod may be locked in place.

In an alternative embodiment as described previously, the tines orwedges of the coupling body that extend upward from the seat for the rodmay be flexible so that they bend or flex around the rod as the cap isturned toward a locking position. For instance, either the cap, thetines or wedges, or both may be configured to have a tapered or rampedsurface that causes gradually increasing radial interference with thecap and coupling element as the cap is rotated. As the radial forcesresulting from this interference increases, the tines or wedges may bendor flex radially inward and press against the elongate rod. One or moredetents and depressions may be placed on either the cap or the couplingbody to hold the cap in a locked position by engaging with each other ata desired cap position. Rotation of the cap in the opposite directionlikewise causes the elongated rod to become unlocked.

In an alternative embodiment, the cap 170 may contain a set screw 180disposed in the cap 170. As described previously and as shown in FIG.29, the set screw 180 disposed in the cap 170 may then apply additionaldownward pressure on the elongate rod 160 to hold it firmly in position.In addition, the downward pressure applied by the set screw 180 may betransferred through the elongate rod 160 onto the coupling wedge 120 andcoupling body components 110 thus locking the coupling element to thefastener head.

In yet another embodiment, a cap 200 is provided that allows the user toeasily insert the cap into the coupling body. For example, withreference to FIGS. 30-32 s, cap 200 is provided that may be placedwithin the coupling body 210. In this embodiment, cap 200 is cylindricalin shape and generally matches the shape of coupling body 210. The cap200 is configured to fit substantially within the interior side walls ofthe coupling body 210. While in the present invention, both the cap 200and coupling body 210 are of substantially cylindrical shape,alternative designs and shapes may be used.

In the embodiment of the FIGS. 30-32, cap 200 contains a lip or rim 220around the exterior circumference of the top or upper portion of cap200. Lip 220 is configured to engage the coupling body 210. The couplingbody may similarly contain a groove 230 disposed about the interiorsurface of the coupling body to interact with the lip 220. The lip andgroove cap design of the present embodiment prevents cap 200 fromtraveling in the longitudinal direction beyond a predetermined positionof the coupling body 210. In this regard, the cap cannot fall into thecoupling body. Without the rim or lip design of the present embodiment,a cap that can fit within the interior of the coupling body may impartdownward force on the elongate rod during insertion of the cap at anundesirable moment. In addition, in instances where the elongate rod isslipped into the coupling body along a latitudinal plane, the presentdesign allows the user to insert the cap prior to positioning orinsertion of the elongate rod because the lip or rim of the cap willprevent the cap from falling into the coupling body and obstructing thespace that is to be occupied by the elongate rod. Another advantageassociated with the lip and groove design is that the cap isself-centering. Another advantage of the present embodiment is that thecap will not interfere with the elongate rod in a locked position.Because the cap resides within the coupling body and remains above theelongate rod, the cap does not require cutouts to allow the cap torotate into a locked position as described previously.

In an alternate embodiment, the coupling body 210 may be designed withone or more channels 240, 242 that are configured to receive protrusions250, 252 on the cap 200. Referring to FIGS. 30-32, the coupling body 210is configured with channels 240, 242 along the interior side walls ofthe coupling body 210. For example, in one embodiment the coupling body210 is comprised of substantially rigid tines 260, 262 that extendupward from the seat for the elongate rod and each tine includes aninterior side wall 261, 263, respectively. Channels 240, 242 are formedon the interior side walls 261, 263 of the upwardly extending tines 260,262. The channels 240, 242 are configured to receive protrusions 250,252 of cap 200.

In the present embodiment, the cap 200 contains tabs or protrusions 250,252 that extend radially outward from the outer circumference of themain cap body. The protrusions 250, 252 may be integrally formed withthe cap 200 or may not be. The protrusions 250, 252 of the cap 200 aredesigned so that upon insertion of the cap 200 into the coupling body210, the protrusions 250, 252 will not interfere with the tines orwedges 260, 262 of the coupling body 210. As seen in FIGS. 31 and 32,the size of the protrusions are of a dimension that allows the cap to beinserted into the coupling body. As seen in FIG. 31, cap 200 is shown ina first position wherein the protrusions 250, 252 are configured toinitially fall within the portion of the coupling body 210 that receivesthe elongate rod, i.e., the openings between the two upwardly extendingarms or tines 260, 262. As described previously, in some embodiments thelip or rim 220 will position the cap 200 at a predetermined locationwithin the coupling body 210. In the embodiment containing a lip or rim220, after placement of cap 200 into coupling body 210 the protrusions250, 252 will lie in the same latitudinal plane as the interior channels240, 242 of the coupling body. To lock the cap into position, the cap isrotated to a second position, as shown in FIG. 32. Upon rotation of thecap, the protrusions 250, 252 of the cap 200 will ride within or fitinside the interior channels 240, 242 of the coupling body.Alternatively, where no lip or rim is present on the cap, the user mayposition the cap by hand until the protrusions align with the channelpresent on the interior side walls of the coupling body. Once aligned,the cap is rotated and the protrusions of the cap ride within theinterior channels of the coupling body.

The channels 240, 242 may be configured to selectively receive theprotrusions 250, 252 when the cap is rotated from a particulardirection. For example, as seen in FIG. 31, channel 240 is configured sothat the cap may only be rotated in on direction. The channelconfiguration of FIG. 31 shows how the channel 240 may be formed so thatthe protrusion 250 may only enter the channels from one direction. Ofcourse, if one channel is configured to receive the protrusion of thecap from one direction, the second channel must be similarly configured.In FIG. 31, the channels 240, 242 are configured to receive theprotrusions 250, 252 when the cap 200 is rotated in the counterclockwise direction. Whether rotation is clockwise or counterclockwise(shown) is not important.

While a number of different design variations may be employed, it may bedesirable to prevent the cap from rotating more than a discretedistance. In this regard, the protrusions may interact with the couplingbody. Alternatively, one or more stops may be provided. In thisalternative embodiment, the stops may be designed so that theprotrusions 250, 252 of the cap 200 will contact or interfere with aportion of coupling body 210 to prevent further rotation of the cap. Inone embodiment, channels 240, 242 may contain a stop configured toprevent the cap from any further rotation after insertion. Accordingly,upon insertion of the cap into the coupling body, the protrusions 250,252 of the cap may ride within channels 240, 242 until the protrusionsinteract with one or more stops. The stop may be formed within thechannel residing on the interior side walls of the coupling body or itmay be positioned elsewhere on the coupling body. Alternativeconstructions may position the stop on the interior side walls of theupwardly extending tines, or alternatively, the stops may be part of thelip and groove portion of the cap and coupling body. In alternativeembodiments, the configuration or design of the channel itself may actas the stop. As seen in FIGS. 31 and 32, the channels 240, 242 do notrun along the entire circumferential length of the inner side walls 261,263 of the upwardly extending tines 260, 262. Accordingly, at area 270,the protrusions 250, 252 will interfere with the interior side walls261, 263 of the tines 260, 262 and further rotation of the cap 200 isprevented. As shown in FIGS. 31 and 32, cap 200 is capable of about 90degrees of rotation. Alternatively, the cap may be rotatable anywherefrom 180 degrees to about 5 degrees.

In an alternative embodiment, for example as shown FIG. 33, the couplingbody may be formed with stops 272, 274. Whether the stops are integrallyformed or not with the coupling body is not important. FIG. 33 showsstops 272, 274 that are not integrally formed with the coupling body. InFIG. 33, the stops 272, 274 are press fit into the coupling body andlaser welded to the coupling body or otherwise fixed in place. As seenin FIG. 33, the stops prevent the cap from rotating in a angulardirection past a desired point. Depending on design considerations, itmay be desirable to rotate the cap from between about 5 degrees to about180 degrees.

As seen in FIG. 33, the stops 272, 274 are designed to protrude radiallyinward from the wall of the coupling body into the channels 240, 242 tocreate a physical barrier against which the cap protrusions 250, 252abut. The stops 272, 274 comprise contact surfaces configured anddimensioned 273, 275 to mate or fit with the protrusions 250, 252. Theprotrusions 250, 252 comprise contact surfaces 251, 253 similarlyconfigured and dimensioned to mate or fit the contact surfaces 273, 275of the stops. In some embodiments, for example as seen in FIG. 33, thecontact surfaces 273, 275 of the stops and the contact surfaces 251, 253of the protrusions are configured to fit, cooperate, mate, or otherwiseengage to prevent angular movement of the cap beyond a predeterminedpoint.

One of the advantages of the aforementioned design of the stops andprotrusions is that after rotation of the cap to its second or lockedposition, the contact surfaces of the stops increase the strength andeffectiveness of the stop by providing a contact surface having a shapeconforming to its respective contacting surface and may further helpprevent the arms of the coupling body from splaying or spreading. Forexample, as seen in FIG. 33, the contact surfaces of the stops are flatsurfaces that are perpendicular to the inner and outer circumference ofthe coupling body. Similarly, the contact surfaces of the protrusionsmay be designed or configured as flat surfaces perpendicular to theinner circumference of the coupling body to mate with or abut the flatcontact surfaces of the stops. In designs where the contact surfaces ofthe stops and protrusions are rounded, force during rotation of the capmay cause the cap to splay or spread the arms of the coupling body. Byconfiguring the contact surfaces of the stops and protrusions as flatsurfaces, the potential for the splaying or spreading of the arms of thecoupling body is significantly reduced. In alternative embodiments thecontact surfaces do not necessarily have to be flat. For example, thecontacting surfaces may be convex and concave or any other design sothat the contact surfaces of the mating pair substantially fit,cooperate, or engage with each other. In general any configuration ofthe contact surfaces may be used such that there is no substantialtorsional force or outward radial force imparted on the stop or couplingbody as a result of the rotation of the cap and its correspondingprotrusions.

In an alternative embodiment, for example as shown in FIG. 34, the stopsmay be designed with contact surfaces at an angle less than 90 degreeswith respect to the interior sidewalls of the coupling body. While onlyone half of the alternative embodiment is shown in FIG. 34, it should beunderstood that the other half of the cap design may be similarlyconfigured. As shown in FIG. 34, the contact surface 253 of theprotrusion 252 is angled with respect to the interior surface of thecoupling body. Similarly, as shown in FIG. 34, the contact surface 275of the stop 274 is angled with respect to the interior surface of thecoupling body. Contact surfaces 253 and 275 are configured and adaptedto mate or engage with each other. Accordingly, when the cap is rotatedto a second or locked position, the mated contact surfaces 253 and 275prevent splaying or the outward radial expansion of the arms of thecoupling body. Additionally, the present configuration increases theoverall structural integrity of the coupling body as well as thestrength of the stop.

As seen in FIG. 35, the contact surfaces 253 and 275 may be angled withrespect to an interior surface 263 of the coupling body. In thisalternative embodiment, the contact surface 253 of the stop is at anacute angle 254 with respect to the interior surface of the couplingbody. In addition, the contact surface 275 of the protrusion is at anobtuse angle 276 with respect to the interior surface 263 of thecoupling body. One of skill in the ordinary art would recognize that therespective angles of the contact surfaces could vary from between about0° and 90° for the stop contact surface and from between about 90° and180° for the protrusion contact surface. Any angle between these valueswould function to substantially eliminate any outward radial force thatmay be imparted upon the coupling body. and stops from the rotation ofthe cap.

Generally, protrusions 250, 252 extend radially outward from the outercircumference of the main cap body and may further be configured oradapted to create an interference or friction fit with the couplingbody. As seen in FIGS. 31 and 32, the protrusions 250, 252 may bedesigned to create a friction or interference fit with the coupling body210. This design allows the cap to be rotated into a locked position. Asshown in FIGS. 31 and 32, each of the protrusions 250, 252 is configuredwith two high points 253, 254 and one low point 255 when viewed in anaxial plane. Each of the channel 240, 242 of the coupling body 210 maybe similarly configured with two high points 243, 244 and one low point245 to match the low and high points of the protrusions. Accordingly,upon rotation of the cap the first high point 254 may interfere with thelow point 245 of the channel. This interference may be overcome withsufficient force. Upon further rotation, the first high point 254 of theprotrusion 250 will fit within the corresponding high point 244 of thechannel. After rotation, the low point 255 of the protrusion 250 isaligned with and/or fits or matches the low point 245 of channel 240. Inthis manner, a friction fit is provided that locks cap 200 intoposition. Additionally, in the embodiment shown in FIGS. 31 and 32 thesecond high point 253 of the protrusion 250 (in conjunction with thedesign of the channel) generally prevents cap 200 from being rotated inthe clockwise direction. Also as shown in FIGS. 31 and 32 the channel240, 242 are configured to prevent further rotation of the cap in thecounterclockwise direction once the cap has been rotated by about 90degrees. Additionally, the cap and/or coupling body may be configured toprovide a tactile feel or audible click when being rotated to a secondor locked position, such as for example the position shown in FIG. 32.In alternative designs, only one of the protrusions may create aninterference fit. Also, in alternative designs, the protrusions may beintegral to the sidewalls of the upwardly extending tines and thechannels may be formed in the body of the cap.

As described previously, cap 200 may also comprise a locking elementcapable of securely holding the elongate rod in a fixed positionrelative to the coupling body. In one embodiment, the cap 200 may have athreaded opening and the locking element may be a threaded set screwdisposed within the threaded opening. As shown in FIGS. 30-32, a setscrew 280 is disposed within cap 200 and may contain a hexagonal cut out282 disposed on the upper portion of the set screw to receive a tool torotate the set screw. In alternative embodiments, other tool interfaceconfigurations may be used. Set screw 280 is capable of applyingdownward force or pressure on the elongate rod to lock the elongate rodin position relative to the coupling body. In this embodiment, generallyany upward force exerted on the cap as a result of the downward forceimparted on the elongate rod by the set screw is counteracted by theprotrusions 250, 252 of cap 200 that lie within channels 240, 242. Theinteraction of the protrusions with the channel counteract the upwardforce and a net resulting downward force is applied to the elongate rod,locking or fixing the elongate rod with respect to the coupling body.

In alternative embodiments, a polyaxial screw design is provided withimproved cap designs. The cap designs are directed at providing easierinstallation of the cap and improved retention of the elongate rod. Insome embodiments, the improved polyaxial cap designs prevent the capfrom rotating out of position after it has been rotated into place. Inother embodiments, the improved cap design provides for greaterstability of the polyaxial screw, including preventing splaying of thearms of the coupling body of the polyaxial screw.

For example, and with reference to FIGS. 36 and 37, an alternatepolyaxial screw design is provided with a coupling body 300 and cap 320.As shown in FIGS. 36 and 37, coupling body 300 contains two upwardlyextending arms 302, 304 that extend longitudinally in the proximaldirection. The coupling body has two slots 310, 311 configured toreceive an elongate rod. Arms 302, 304 of coupling body 300 haveinterior and exterior surfaces. Interior surfaces 303, 305 of arms 302,304 respectively are configured with inwardly projecting radialprotrusions 306, 307, 308, and 309. Coupling body 300 is also designedwith a lip or rim that resides on the upper surface of the couplingbody. As seen in FIGS. 36 and 37, each arm 302, 304 of coupling body 300has disposed about its superior surfaces 312, 313 a partiallycircumferential rim 314, 315, respectively. The rims 314, 315 haveexterior surfaces 316, 317 that interact with the cap as described inmore detail below.

As further seen in FIGS. 36 and 37, cap 320 of the present embodimentcomprises an upper portion 325 that is generally circular in shape. Theupper portion 325 has a central hole 330 that is adapted to receive aset screw (not shown). Two arms 332, 334 extend downward from the cap'supper portion 325. Each arm 332, 334 of cap 320 is configured withradially outwardly extending protrusions that are designed to interactwith the inwardly extending protrusions 306, 307, 308 and 309 ofcoupling body 300.

With continuing reference to the embodiments shown in FIGS. 36 and 37,FIG. 38 illustrates a partial view of a cap design of the presentinvention. As seen in FIG. 38, the exterior perimeter 336 of arm 332 isoffset radially inward with respect to perimeter 338 of upper portion325. Disposed along the exterior perimeter 336 of arm 332 are twooutwardly extending radial protrusions 340, 342. Outwardly extendingradial protrusions 340, 342 are configured to fit within spaces createdby inward facing protrusion 306, 307 of coupling body 300 upon insertionof cap 320 onto coupling body 300, e.g., when cap 320 is moved along thelongitudinal axis. As seen in FIGS. 36-38, protrusions 340,342 of cap320 are designed with superior surfaces 341, 343 that interact with theinferior surfaces of the corresponding inwardly projecting protrusionsof coupling body 300, in this case, inwardly projecting protrusions 306,307 of coupling body 300. As one of skill in the art would understand,arm 334 similarly has outwardly extending radial protrusions 350, 352(best seen in FIG. 37) that similarly interact with their correspondinginwardly extending radial protrusions, i.e. 308, 309 of coupling body300. In some embodiments, the contact surfaces of the protrusions may bedesigned to provide an interference fit, a friction fit, a tongue andgroove fit, or other known interaction fits that lock or prevent the capfrom rotating out of the closed position. As seen in FIG. 36, theinferior and superior surfaces of the protrusions may also be designedwith sloped surfaces that upon rotation of the cap into the closedposition, prevent arms 302, 304 of the coupling body 300 from splaying.

With continuing reference to FIGS. 36-38, upper portion 325 of cap 320is configured with a retaining edge about the inferior perimeter of theupper portion 325. With reference to FIG. 38, the inferior surface 346of upper portion 325 is configured with a retaining edge 348. Retainingedge 348 is configured to interact with rim 314 of coupling body 300.Upon insertion of the cap onto the coupling body 300, retaining edge 348engages rim 314 of coupling body 300. This design feature of the presentembodiment provides stability to coupling body 300, and moreparticularly, may radially capture arm 302 or prevent splaying of arm302.

As further seen in FIG. 39, cap 320 may be rotated into a second orclosed position. In the closed position, the retaining edges 348(hidden) and 349 of upper portion 325 contact rims 314, 315 of couplingbody 300. As further illustrated by FIG. 39, in its closed positioninwardly extending radial protrusions 306-309 of coupling body 300 aresimilarly engaged with the outwardly extending radial protrusions 340,342, 350, and 352 of arms 332, 334 of cap 320 respectively and aspreviously described. With reference to FIG. 40, a partial close-up viewof cap 320 and coupling body 300 is shown. FIG. 40 illustrates theinteraction between rim 315 of coupling body 300 and retaining edges354, 356 of upper portion 325 of cap 320 when cap 320 is in the secondposition.

FIG. 39 further illustrates another feature of an embodiment of thepresent invention. With reference to FIG. 39, upper portion 325 of cap320 resides substantially above coupling body 300. Upper portion 325 maybe designed with flat surface 355. Accordingly, these opposing flatsurfaces may be used as engagement surfaces for a tool to grasp cap 320.Furthermore, as one of skill in the art would understand, tools designedto engage the flat surfaces of upper portion 325 of cap 320 may be usednot only to insert cap 320 into coupling body 300 but also to rotate cap320 into a second or closed position. Additional embodiments contemplatethe use of alternative engagement surfaces and mechanisms to allow toolsto insert and rotate the cap.

As described previously, when the cap is in the second or closedposition, the cap may be locked or otherwise prevented from beingrotated into the first or open position. As one of skill in the artwould understand, any variety of mechanical means may be employed toprevent the cap from rotating from the second or closed position to thefirst or open position. For example, interference or friction fits maybe designed into any number of components of the cap and coupling body.Alternatively, separate components such as pins, screws, wedges, etc.may be used to lock, secure, or otherwise prevent rotation from thesecond position to the first position. One such non-limiting example isthe use of a set screw to lock the cap into position. Upon insertion ofthe cap and rotation into its closed position, a set screw may be usedto lock all components of the polyaxial screw. As previously described,the set screw may lock the coupling body and fastener into a fixedposition. In addition, the force of the set screw can lock the cap intoits closed position via the counteracting force of the inward andoutward protrusions of the cap and coupling body.

Referring to FIGS. 41-46, another embodiment of the present invention isprovided. With reference to FIG. 41, cap 400 and coupling body 420 areshown. In this embodiment of the present invention, cap 400 comprises anupper portion 402 and lower portion 402. As can be seen from FIG. 41,cap 400 is generally cylindrical in shape. With continuing reference toFIG. 41, coupling body 420 is illustrated. In an embodiment of thepresent invention, coupling body 420 contains two upwardly extendingarms 422, 424 that extend longitudinally in the proximal direction. Thecoupling body has two slots 426, 428 configured to receive an elongaterod (not shown). Arms 422, 424 of coupling body 420 have interior andexterior surfaces. The interior surface 430, 432 of arms 422, 424respectively are configured with a channel or groove. In FIG. 41, onlychannel or groove 434 is shown, whereas the corresponding channel orgroove 436 on arm 424 is not visible.

With continuing reference to the embodiment of FIG. 41, FIG. 42illustrates cap 400 of the present embodiment. As can be seen in FIG.42, cap 400 has a centrally located bore hole 406 which is configured toreceive a set screw. Cap 400 also has an upper portion 402 and lowerportion 404. Upper portion 402 is generally cylindrical in shape and hasa perimeter portion 408 that is generally circular in shape. As can beseen in FIG. 42, perimeter 408 of upper portion 402 of cap 400 may beformed with a flat or substantially linear portion 41 0 that is notgenerally circular in shape. Linear portion 4 1 0 of perimeter 408 maybe used as an engagement point where a tool may engage cap 400. Toolsmay be used to grasp and insert cap 400 into coupling body 420.

As further seen in FIG. 42, lower portion 404 extends in the distaldirection from upper portion 402. Lower portion 404 is generallycylindrical in shape and has a perimeter 412 offset radially inward withrespect to perimeter 408 of upper portion 402. Lower portion 404 has twosidewalls 414, 416 that are generally linear or flat and are located onopposing sides of lower portion 404. Between opposing sidewalls 414, 416are two generally circular sidewall portions 418, 419. Tongues 423, 425extend radially from the generally circular sidewall portions 418, 419of cap 400. Tongues 423, 425 run generally the entire length orperimeter of the sidewall portions 418, 419 of lower portion 404 of cap400.

Referring to FIG. 43, a cross-sectional view of cap 400 of the presentembodiment is illustrated. As can be seen in FIG. 43, tongues 423, 425extend radially from sidewall portions 418, 419 of lower portion 404 ofcap 400. Tongues 423, 425 may be configured with a rounded orcylindrical profile. Thus, for example as one moves radially from theexterior perimeter 418 of lower portion 404 the profile of tongue 423increases in both the proximal and distal direction. At its outermostportion, the profile of tongue 423 decreases until it becomes a flatedge, creating a partial cylindrical profile as seen in FIG. 43. Thisprofile generally creates two interior engagement surfaces 427, 429 ontongue 423, which extend along tongue 423. While the discussion hasfocused only on tongue 423, one of skill in the art would understandthat tongue 425 has a similar profile as seen in FIG. 43. In alternativeembodiments, the profile of tongues 423, 425 may differ, including butnot limited to, angular profiles with sloping surfaces, non-symmetricalsurfaces, and straight, linear or generally perpendicular profiles.

FIG. 43 further illustrates opening or bore hole 406 that extendslongitudinally through cap 400. While not shown in this particularembodiment, in some embodiments bore hole 406 may have threads along theinterior surface of bore hole 406, which may be designed to engage a setscrew. Alternative embodiments contemplate use of other fasteningdevices known in the art that may interact with bore hole 406 of cap400.

Referring to FIG. 44 a cross sectional view of coupling body 420 of anembodiment of the present invention is shown. As seen in FIG. 44,coupling body 420 comprises two upwardly extending arms 422, 424 thatextend longitudinally in the proximal direction. The coupling body hastwo slots configured to receive an elongate rod (not shown). Arms 422,424 of coupling body 420 have interior and exterior surfaces. Interiorsurface 430, 432 of arms 422, 424 respectively are configured withchannels or grooves 434, 436. As can be seen in FIG. 44, groove 434contains a profile that is slightly larger than the profile of tongue423. Groove 434 extends substantially along the entire interior surface430 of arm 422 of coupling body 420. Similarly, groove 436 contains aprofile that is slight larger than the profile of tongue 425. Groove 436also extends substantially along the entire interior surface 432 of arm424 of coupling body 420. As with the discussion pertaining to tongues423, 425, the profiles of grooves 434, 436 create engagement surfaces.Accordingly, groove 434 contains engagement surfaces, which extend theentire length of groove 434. Similarly, groove 436 contains engagementsurfaces, which extend the entire length of groove 436.

Referring to FIG. 45, cap 400 is shown inserted into coupling body 420.As seen in FIG. 45, cap 400 is in a first position, wherein insertion isaccomplished by moving cap 400 longitudinally downward into couplingbody 420. Tongues 423, 425 are dimensioned to fit within slots 426, 428respectively when cap 400 is inserted into coupling body 420. Inferiorsurfaces 438, 440 of upper portion 402 of cap 400 are designed tocontact upper surfaces 441, 442 of arms 422, 424 respectively ofcoupling body 420. The interaction between these surfaces places cap 400at a predetermined location along the longitudinal axis of coupling body420. As seen in FIG. 45, tongues 423, 425 are positioned such that theyare aligned with grooves 434, 436 of coupling body 420 when cap 400 isinserted into coupling body 420.

Referring to FIG. 46, a cap 400 is illustrated in a second positionwherein cap 400 has been rotated after insertion into coupling body 420.As seen in FIG. 46, tongue 423 fits within groove 434. As cap 400 isrotated from a first position to a second position, tongues 423, 425ride within corresponding grooves 434, 436. As described previously anynumber of stop or limiting mechanisms may be used to prevent cap 400from rotating past a certain point and/or from rotating back into thefirst position once the second position has been reached.

As one of skill in the art would understand, one feature associated withthe present embodiment is the ability of the present design to preventsplaying of the arms. In the second position, engagement surfaces 427,429 of tongue 423, contact or may potentially engage engagement surfacesof groove 434. Similarly, tongue 425 contains engagement surfaces thatcontact or may potentially engage engagement surfaces of groove 436.Accordingly, the interaction between the aforementioned engagementsurfaces can prevent splaying of arms 422 and 424 by virtue of theengagement of said surfaces. This feature adds structural rigidity tothe polyaxial screw design. In addition to the prevention of splaying ofthe arms, the tongue and groove design of the present embodiment maylock or fix the polyaxial screw when desirable. For example, and asdiscussed previously, a set screw may be used to exert a downward forceon the elongate rod. The counteracting upward force on the set screw istransmitted to the tongues of cap 400. As tongues 423, 425 lie withingrooves 434, 436, the counteracting force transmitted to tongues 423,425 causes tongues 423, 425 to engage with grooves 434, 436, thuslocking or fixing the cap, elongate rod, and coupling body in place withrespect to the fastener as described previously.

While the embodiment shown in FIGS. 41-46 is one in which the profile ofthe tongues and grooves are generally spherical in shape, one of skillin the art would understand that a variety of alternate profiles couldbe used. Any number of shapes, including generally linear profiles,perpendicular profiles, non-symmetrical profiles, etc. can be used toeither prevent splaying of the arms and/or serve as a locking mechanismfor the elongate rod and polyaxial screw.

Referring to FIGS. 47-53, another embodiment of the present invention isprovided. With reference to FIG. 47, cap 500 and coupling body 520 areshown. In this embodiment of the present invention, cap 500 has agenerally cylindrical shape. As seen in FIG. 47, cap 500 has twoopposing generally linear side portions 502, 504. Two flange portions506, 508 extend longitudinally in a distal direction. Disposed centrallywithin cap 500 is a central portion 510 extending distally in alongitudinal direction. In an embodiment of the present invention,coupling body 520 contains two upwardly extending arms 522, 524 thatextend longitudinally in the superior direction. The coupling body hastwo slots 526, 528 configured to receive an elongate rod (not shown).Arms 522, 524 of coupling body 520 have interior, exterior, and uppersurfaces. The upper surfaces 530, 532 of arms 522, 524 respectively areconfigured with tongues 534, 536, which are made with a profilediscussed in more detail below.

Referring to FIG. 48, cap 500 of the present embodiment is illustrated.As can be seen in FIG. 48, cap 500 has a centrally located bore hole501, which is configured to receive a set screw. Cap 500 is generallycylindrical in shape. Cap 500 also may have two generally linear faces502, 504 that oppose each other. Linear faces 502, 504 may be used as anengagement points for a tool to grip cap 500. Tools may be used tograsp, insert, and rotate cap 500 into coupling body 520.

As further seen in FIG. 48, two flanges extend longitudinally in andistal direction from cap 500. Flanges 506, 508 have interior andexterior surfaces that are curved and follow an arcuate path thatcorresponds generally to the generally cylindrical external perimeter ofcap 500. Central portion 510 extends longitudinally in a distaldirection and is generally cylindrical in shape. Surfaces 512, 514 ofcentral portion 510 generally correspond to the cylindrical shape offlanges 506, 508 and similarly follow an arcuate path in acircumferential direction about the central axis of cap 500. Centralportion 510 also has two opposing generally linear or flat faces 516,518 that are offset radially inward with respect to linear or flat faces502, 504 of cap 500. Flange 506, and more particularly interior surface507, and cylindrical surface 512 of central portion 510 define a grooveor channel 515. Accordingly, groove 515 is generally cylindrical inshape and extends in an arcuate path that generally corresponds to thecylindrical shape of cap 500. Similarly, flange 508, and moreparticularly interior surface 509, and cylindrical surface 514 ofcentral portion 510 define a second groove or channel 517. Accordingly,groove 517 is. generally cylindrical in shape and extends in an arcuatepath that generally corresponds to the cylindrical shape of cap 500.

Referring to FIG. 49, a cross sectional view of cap 500 of an embodimentof the present invention is shown. More particularly, FIG. 49illustrates the profile of grooves 515, 517 of cap 500. Additionally,bore hole 501 is seen extending through cap 500. Bore hole 501 may beconfigured to receive a set screw by including threads (not shown) onthe interior surface 503 of bore hole 501.

As seen in FIGS. 47-49; grooves 515 and 517 created by central portion510 and flanges 506 and 508 respectively, may be made with variousalternate profiles. In this embodiment of the present invention, grooves515, 517 have a generally circular profile. Because grooves 515, 517partially extend about a circumference spaced from central axis 505 ofcap 500, the circular profiles create grooves that are generally curvedcylindrical spaces.

Referring to FIGS. 50 and 51, a coupling body of the present embodimentis shown. As seen in FIGS. 50-51, coupling body 520 contains twoupwardly extending arms 522, 524 that extend longitudinally in thesuperior direction. The coupling body has two slots 526, 528 configuredto receive an elongate rod (not shown). Arms 522, 524 of coupling body520 have interior, exterior, and upper surfaces. As seen in FIGS. 50-51,arms 522, 524 are generally curved. The upper surfaces 530, 532 of arms522, 524 are shaped with a profile to match the profile of grooves 515,517, creating tongues 534, 536. Accordingly, as seen in FIG. 51 a crosssectional view of arms 522, 524 show the upper surfaces of the arms witha circular profile that matches or generally corresponds to the profileof grooves 515, 517 of cap 500.

With continuing reference to FIGS. 47-51, FIG. 52 illustrates cap 500inserted into coupling body 520. As seen in FIG. 52, cap 500 is in afirst position, wherein insertion is accomplished by moving cap 500longitudinally downward into coupling body 520. Central portion 510 andflanges 506, 508 are dimensioned to fit within slots 526, 528 when cap500 is inserted. As seen in FIG. 52, grooves 515, 517 are positionedsuch that when cap is in the first position, grooves 515, 517 arealigned with tongues 534, 536 of coupling body 500.

With continuing reference to FIGS. 47-52, FIG. 53 illustrates cap 500 ina second position wherein cap 500 has been rotated after insertion intocoupling body 520. As seen in FIG. 53, tongues 534, 536 fit withingrooves 515, 517 respectively. As cap 500 is rotated from a firstposition to a second position, tongues 534, 536 ride withincorresponding grooves 515, 517. As described previously any number ofstop or limiting mechanisms may be used to prevent cap 500 from rotatingpast a certain point and/or from rotating back into the first positiononce the second position has been reached.

As one of skill in the art would understand, one feature associated withthe present embodiment is the ability of the present design to preventsplaying of the arms. In its second position, the tongue and groove fitprevents splaying of arms 522, 524 by virtue of the configuration of thetongue and groove design. In addition to the prevention of splaying ofthe arms, the tongue and groove design of the present embodiment locksor fixes the polyaxial screw when desirable. For example, and asdiscussed previously, a set screw may be used to exert a downward forceon the elongate rod. The counteracting upward force on the set screw istransmitted to cap 500. The tongue and groove design of the presentembodiment counteracts the downward force of the set screw causing thetongues to engage the grooves, thus locking or fixing the cap, elongaterod, and coupling body in place with respect to the fastener asdescribed previously.

While the embodiment shown in FIGS. 47-53 is one in which the profile ofthe tongues and grooves are generally curved cylinders in shape, one ofskill in the art would understand that a variety of profiles could beused. Any number of shapes, including substantially linear profiles,perpendicular profiles, non-symmetrical profiles, etc. can be used toeither prevent splaying of the arms and/or serve as a locking mechanismfor the elongate rod and polyaxial screw.

Referring to FIGS. 54-61, another embodiment of the present invention isprovided. With reference to FIG. 54, a polyaxial screw assembly 500 isshown having a cap 510, a coupling body 520, and a fastener 530. As canbe seen in FIG. 55, cap 510 is generally cylindrical in shape. Along aperimeter sidewall 511 of the generally cylindrical cap 510 are twoprotrusions 512, 514 (not visible). Each protrusion partially extendsabout the circumference of the cap sidewall 511. Protrusions 512, 514are disposed along sidewall 511 in a position such that upon insertion,protrusions 512, 514 can be rotated into the coupling body channels 534,536 as discussed below. As can be further seen in FIG. 55, the cap maybe formed with a partial lip or rim. In this embodiment, cap 510 isformed with two rims 516, 518, which extend radially outward from thetop end of the perimeter of cap 510.

Referring to FIG. 55, coupling body 520 is also illustrated. In anembodiment of the present invention, coupling body 520 contains twoupwardly extending arms 522, 524, which extend longitudinally in thesuperior direction. The coupling body has two slots 526, 528 configuredto receive an elongate rod (not shown). Arms 522, 524 of coupling body520 have interior and exterior surfaces. The interior surfaces 523, 525of arms 522, 524 respectively are configured with a channel or groove.In FIG. 55, only channel or groove 534 is shown, whereas thecorresponding channel or groove 536 on arm 524 is hidden. Also seen inFIG. 55 are recesses 527, 529 formed in the upper surfaces 531, 533 ofarms 522, 524. Recesses 527, 529 extend interior to the sidewalls 523,525 of arms 522, 524. Recesses 527, 529 are designed to accept the lipsor rims 516, 518 of the cap 510 when the cap is inserted into couplingbody 520. In this manner, the design provides a mechanism or featurethat positions the cap in a predetermined location in the longitudinaldirection after insertion into the coupling body. The positioningfeature of the present embodiment aligns the protrusions of the cap withthe channels of the coupling body.

Referring to FIG. 56, interior sidewall 523 of coupling body 520 isseen. As seen in FIG. 56, channel 534 is formed within interior sidewall 523 and partially extends along the interior perimeter of sidewall523. At the proximal end, channel 534 is open and accessible from slot526. At the distal end, channel 534 terminates prior to slot 528. As oneof skill in the art would understand, corresponding channel 536 issimilarly configured, except that channel 536 is open and accessiblefrom slot 528 and terminates prior to reaching slot 526.

The height of channels 534, 536 are dimensioned to correspond to thethickness or height of protrusions 512, 514. Additionally, as seen inFIG. 56, channel 534 has a relief area at the termination end of channel534. Relief area 535 is formed by a cavity that is radially larger thanchannel sidewall 539. As described in more detail below, relief area 535interacts with protrusion 514 when cap 5 10 is rotated into a closedposition. As one of skill in the art would understand, correspondingchannel 536 is similarly configured except that relief area 537 (hidden)is located at the termination end of channel 536.

Referring to FIG. 57, an exploded view of cap 510 and coupling body 520is shown. The cap 510 is configured to partially fit within couplingbody 520. Protrusions 512, 514 (not visible) are sized such thatprotrusions 512, 514 fit within slots 526, 528 as cap 510 is insertedinto coupling body 520. As described previously, as the cap is inserted,rims 516, 518 abut recesses 527, 529, thereby stopping cap 510 at apredetermined longitudinal position within coupling body 520. At theinsertion position, the protrusions 512, 514 are aligned with channels534, 536. Protrusions 512, 514 are sized such that upon rotation of thecap, the protrusions will ride within corresponding channels 534, 536.As also seen in FIG. 57, protrusion 534 is configured with two highpoints 541, 543 and one low point 542. High points 541, 543 provideinterference points when cap 510 is rotated into channel 534; low point542 provides a relief point when the cap is rotated past theinterference point and is in its closed position. While not shown inFIG. 57, one of skill in the art would understand that the interiorsidewall of channels 534, 536 are configured with a high point.Accordingly, as the cap is rotated into position, high point 541interferes with the high point of channel 534. These interferencepoints, however, may be designed such that a user may overcome theinterference with sufficient force, allowing the cap to rotate into afinal position, wherein the high point of the interior sidewall 539 ofthe channel 534 fits within the low point 542 on protrusion 512. Thisinterference fit prevents the cap from rotating back into the openposition. While the present embodiment utilizes high and low pointsalong the contacting surfaces of the protrusions and channels, one ofskill in the art would understand that any variety of interference fitsor friction fits may be used to prevent the cap from rotating back intothe open position.

Referring to FIGS. 58 and 59, a partial top view of the cap and couplingbody is shown. With the cap inserted and in the open position (FIG. 58),protrusions 512, 514 lie within the space created by slots 526, 528. Ascan be seen in FIG. 58, channel 534 is open to slot 526 and channel 534is open to slot 528. Accordingly, as the cap is rotated clockwise,protrusions 512, 514 will enter channels 534, 536, respectively. As seenin FIG. 59, cap 510 has been rotated to the closed or second position.In FIG. 59, protrusions 512, 514 are within channels 534, 536.

With continuing reference to FIGS. 58 and 59, relief areas 545, 547 areshown. Relief areas 545, 547 are cavities formed within the interiorchannels 534, 536. Relief areas 545 and 547 provide an area in whichleading edges 546, 548 of protrusions 512, 514 respectively may residewhen cap 510 is rotated into the second position. As can be seen in FIG.59, leading edges 546,548 reside within relief areas 545,547,respectively. The relief areas allow the cap to be rotated a full 90°.Without relief areas 545, 547, the leading edges 546, 548 would comeinto contact with interior channel walls and impart a radially outwardforce on arms 522, 524 of coupling body 520. This net radial outwardforce would impart unwanted forces on the coupling body and may lead toincreased splaying of arms 522, 524 when cap 510 is rotated into itssecond or closed position.

In addition to the anti-splay features, relief areas 545, 547 andleading edges 546, 548 may be designed to provide a mechanical stop. Asseen in FIG. 59, when cap 510 is rotated to its closed position, leadingedges 546, 548 abut or contact walls 549, 550 of relief areas 545, 547.This contact limits rotation of the cap and prevents the cap fromrotating past about 90°. As one of skill in the art would understand,the relief area may be configured in any number of fashions toaccommodate the corresponding leading edges of the protrusions.Similarly, the size or length of the channels and protrusions may vary,however, one advantage of the present embodiment is the large surfacearea of the protrusions and channels. This surface area provides forgreater contact between the coupling body and the protrusions of thecap, imparting greater strength and stability to the overall polyaxialscrew assembly.

FIG. 60 provides an illustration of the fastener 530, coupling bodycomponents 550 and wedge 560. As previously described, the force of anelongate rod (not shown) exerting downward pressure on wedge 560 drivesthe coupling body components 550 to tighten around head 535 of fastener530. This assembly, as previously described, locks the variouscomponents of the polyaxial screw in a fixed position. Thus, while thecoupling body remains free to move about head 353 of fastener 530 priorto the final implantation of the elongate rod, once the components aretightened, the polyaxial screw components become generally fixed inorientation with respect to each other.

As seen in FIG. 61, the cap 510 has a central bore hole 570. A set screw580 may be provided. In FIG. 61, the set screw 580 is externallythreaded (not shown) and the corresponding bore hole 570 is internallythreaded (not shown). Upon insertion of the elongate rod and then thecap, the set screw may be used to tighten the various components of theassembly. In this manner, the set screw exerts downward pressure on therod, which in turn exerts downward pressure on the wedge, coupling bodycomponents, and wedge. The cap (and the tongue and groove fits of theprotrusions and channels) counteract the counteracting upward force thatis experienced by the assembly as a result of the pressure exerted bythe set screw. This allows the set screw to create a net downward forceto lock the elongate rod, coupling body, and fastener together in agenerally fixed orientation.

While the previous embodiment has been shown and described with certainsizing and shape parameters, one of skill in the art would understandthat any variety of modifications could be made to achieve similarresults. For example, while in the previously described embodiments, thecap is rotated in the clockwise direction, the direction of rotationcould easily be changed with modifications to the channels and/orprotrusions. Similarly, while the protrusions are shown extending alongthe perimeter of the cap sidewalls, the length of the protrusions inalternative embodiments could vary. By way of yet another example, therelief areas and leading edges of the channels and protrusions areconfigured to allow the cap to rotate 90°. Yet, one of skill in the artwould readily appreciate that simple design changes could be made tovary the amount of rotation required to place the cap in the second orclosed position.

Additional features may be associated with any number of theaforementioned designs. For example, one feature that may be integratedinto the previously described embodiments include engagement areas fortools or other apparatus.

Referring to FIG. 62, one such feature is displayed. In FIG. 62,coupling body 600 is shown with two upwardly extending arms 602, 604.Disposed about exterior surfaces 603, 605 of coupling body 600 areengagement areas 606, 608. In this embodiment, engagement areas 606, 608may be configured or designed to engage with tools or other apparatus.One such example of a tool or apparatus is a reduction device, which maybe used by a surgeon during implantation of the elongate rod to reducethe space between seat 610 of coupling body 600 and the elongate rod(not shown). Other examples of tools or apparatus that may engage withengagement areas 606, 608 include positioning devices, minimallyinvasive system tools, insertion tools, holding apparatus, aligningdevices, etc.

As seen in FIG. 62, engagement areas are formed within the exteriorsidewalls 603, 605 of coupling body 600. Engagement area 608 has theshape of a generally rectangular channel 611, which runs along ahorizontal axis from slot 612 to slot 614. Channel 611 may be designedwith additional engagement areas. For example, disposed at sidewalls613, 615 of channel 611 are semicircular areas 616, 618. Semicircularareas 616, 618 are formed in the exterior surface 605 of arm 604 ofcoupling body 600, and may be approximately of the same depth as channel611. Semicircular areas 616, 618 may provide an additional engagementarea for a tool or apparatus. For example, a reduction device, may beconfigured with a round pin or head that engages with the engagementarea 608. Furthermore, sidewalls 613, 615 may be formed with back cutssuch that they create an angled surface against which tools or otherdevices may engage. As one of skill in the art would understand,exterior surface 603 of arm 602 of coupling body 600 may similarly beconfigured with an engagement area 606. Accordingly, a tool may engagewith both arms 602, 604 for rod reduction, positioning, alignment, etc.

Embodiments of the present invention do not contemplate any oneparticular engagement design. Engagement areas may be placed in anynumber of positions and may take the form of any number of shapes orconfigurations. For example and as seen in FIG. 63, one alternativeembodiment contemplates the use of bore holes 621, 623 disposed on eachof the arms 602, 604 of coupling body 600. Alternatively, holes 621, 623may be blind holes or holes that do not open to the interior surfaces ofcoupling body 600. In an alternate embodiment and with reference to FIG.64, holes 625, 627 may be located on the coupling body 600 below slots612, 614. As seen in FIG. 64, holes 625, 627 are shown disposed belowslots 612, 614 and do not extend to the interior surface of couplingbody 600. In alternate embodiments, holes 625, 627 are bore holes andextend through coupling body 600.

In an alternate embodiment and as seen in FIG. 65, engagement areas 631,633, 635, and 637, may be formed on arms 602, 604 of coupling body 600.Referring to FIG. 65, each arm 302, 304 is configured with twoengagement areas, 631, 633 and 635, 637, respectively. Engagement areasmay take any number of shapes and may extend into the coupling body byvarying amounts, however, the purpose of said engagement areas is toprovide an interfacing area at which a tool or other device may engagewith said areas and transfer forces to the coupling body, elongate rod,cap, etc. Engagement area 631, in this particular embodiment, is shapedas an extruded cylinder within the sidewall 632 of arm 602. Engagementarea 631 is formed into arm 602 of coupling body 600 to a particulardepth. While only one engagement area is described, it should beunderstood that in this embodiment, each engagement area 631, 633, 635,637 is similarly configured.

In an alternate embodiment and as seen in FIG. 66, coupling body 300 maybe formed with engagement areas 641, 643 which take the form of channelsdisposed about the exterior surfaces 603, 605 of arms 602, 604 ofcoupling body 600. These channels may differ from those previouslydescribed in that as the channels approach slots 612, 614, the channelsmay be formed at an angle that is tangential to the generally circularshape of the coupling body. Similarly, but of an alternate design,coupling body 600 may have four engagement areas disposed on each arm602, 604. As seen in FIG. 67, in this alternate embodiment, engagementareas 651, 653, 655, 657 are tangential slots that run along ahorizontal axis and are disposed at the proximal and distal ends of arms602, 604.

Referring to FIG. 68, coupling body 600 may be formed with bore holes661, 663, 665, and 667. As seen in FIG. 68, bore holes 661, 663, 665,667 are disposed about the superior surfaces 662, 664 of arms 602, 604.Holes 661, 663, 665, and 667 extend longitudinally in the inferiordirection. Because the coupling body is tapered, the holes extendthrough the coupling body forming openings 666, 668, 670, and 672 at thelower end of the coupling body. Openings 666, 668, 670, and 672 provideengagement areas for tools or other apparatus. Similarly, openings 661,663, 665, and 667 at superior surfaces 662, 664 may be provideengagement areas for devices, apparatus, or tools.

Additional features may be associated with any number of theaforementioned designs. For example, the cap of the polyaxial screwassembly may be designed to aid the surgeon during implantation of theassembly. One such feature may include a cap with a unique lower surfacethat interacts with the elongate rod during insertion. Referring to FIG.69, a polyaxial screw assembly of the present invention is shown. Asseen in FIG. 69, cap 700 has an inferior surface 702 which contains adepression area 704 that generally corresponds to the curvature of uppersurface 706 of elongate rod 708. Accordingly, when cap 700 is insertedinto coupling body 710 in a first position, cap 700 exerts some downwardpressure on elongate rod 708. As further seen in FIG. 69, upper surface706 of elongate rod contacts lower surface 702 of cap 700 and elongaterod 708 partially fits within depression area 704 of cap 700.

Turning to FIG. 70, cap 700 has been rotated to its second or closedposition. As one of skill in the art would understand, upon rotation ofcap 700 from its first position to its second position, the unique shapeof the lower surface 702 of cap 700 drives the elongate rod down intocoupling body 710. This clamping action of cap 700 aids the surgeon inreducing elongate rod 708. The downward force applied to elongate rod708 by cap 700 positions elongate rod 708 further into coupling body 710and increases the ease with which the entire polyaxial screw assembly isimplanted into a patient.

As illustrated by the many embodiments described above, the presentinvention is capable of providing greater flexibility for the physicianfor installing and adjusting a spinal fixation system. In practice, thephysician installs a plurality of fasteners to the treated area of thespine. The fasteners 20 are configured with coupling elements 26 thatcan be moved and rotated into several positions. The physician may lockin a desired position for the coupling element 26 without requiring theelongated rod to also be locked in position. Likewise, the physician mayunlock coupling element 26 from the fastener 20 even after the rod hasbeen locked to the coupling element. Thus, the physician is free toreadjust the rotation and angle of the coupling element 26 with respectto the fastener 20 at any time.

In sum, the embodiments described above show that the present inventionprovides several advantages not previously achieved by the prior art.For instance, one advantage realized by allowing independent locking andunlocking of the rod locking device and the coupling locking device isthat the polyaxial screw permits significantly greater adjustabilitythan could be accomplished in the past. Adjustment of the connectionbetween the rod and the coupling device need not risk losing a desiredpositioning of the coupling element with respect to the screw. Thus, thepresent invention allows for fine tuning whereas prior systems requiredwere designed to loosen all of the components in order to reposition anycomponent.

In addition to providing greater adjustability, the present inventionalso reduces the complexity and number of the surgical steps involvedfor installing a spine stabilization system. The present invention alsoprovides for a more compact design than could be achieved in the past,and reduces the number of separate pieces associated with the implant.Altogether, these advantages will help reduce intra operative time,simplify the surgical procedure, and work well in a wider variety ofpatient anatomy.

While it is apparent that the invention disclosed herein is wellcalculated to fulfill the objects stated above, it will be appreciatedthat numerous modifications and embodiments may be devised by thoseskilled in the art. Therefore, it is intended that the appended claimscover all such modifications and embodiments that fall within the truespirit and scope of the present invention.

What is claimed is:
 1. A spine stabilization system comprising: anelongate rod; a bone fastener having a rounded head; a coupling elementcomprising a coupling body and a cap; wherein the coupling bodycomprises sidewalls that define two upwardly extending arms which definetwo slots capable of receiving the elongate rod; wherein the couplingbody and cap interact to capture the elongate rod in the coupling body,wherein a first and second protrusions configured on opposing sides ofthe cap and extending in a radial direction and a first and secondrecess configured in the two upwardly extending arms extending in aradial direction and wherein the first and second protrusions areconfigured and dimensioned to engage the first and second recess tolimit movement of the cap with respect to the coupling body, when thecap is rotated from a first position to a second position, wherein thecap having a threaded opening for receiving a threaded locking element,the locking element capable of securely holding the elongated rod in afixed position relative to the coupling element, wherein the cap furthercomprises at least one rim which extends radially outward from the topend of the perimeter of the cap, wherein a first of the upwardlyextending arms includes a third recess positioned between the firstrecess and the upper surface of the first of the upwardly extending armsfor receiving the at least one rim of the cap and a second of theupwardly extending arms includes a fourth recess for receiving the atleast one rim of the cap, the fourth recess positioned between thesecond recess and the upper surface of the second of the upwardlyextending arms and wherein the third recess extends along the length ofan inner surface of the first of the upwardly extending arms and thefourth recess extends along the length of an inner surface of the secondof the upwardly extending arms.
 2. The spine stabilization system ofclaim 1, wherein the at least one rim engages the upwardly extendingarms to align the first and second protrusion s of the cap and the firstand second recesses of the coupling body when the cap is inserted intothe coupling body.
 3. The spine stabilization system of claim 1, whereinthe height of the first and second recesses are dimensioned tocorrespond to the thickness of the first and second protrusion.
 4. Thespine stabilization system of claim 3, wherein the first and secondrecesses are configured with a first and second relief area.
 5. Thespine stabilization system of claim 4, wherein the first and secondrelief areas interact with the first and second protrusion when the capis rotated into a final position.
 6. The spine stabilization system ofclaim 1, wherein the cap comprises a lower surface configured to exertdownward force upon the elongate rod as the cap is rotated from a firstposition to a second position.
 7. A spine stabilization systemcomprising: an elongate rod; a bone fastener having a rounded head; acoupling element comprising a coupling body and a cap; wherein thecoupling body comprises sidewalls that define first and second upwardlyextending arms, said arms defining two slots capable of receiving theelongate rod; wherein the cap comprises an upper portion and a lowerportion, the upper portion of the cap having radially extending firstand second protrusion; wherein the first upwardly extending armcomprises a first recess and a first channel, the first recessconfigured to engage with the first protrusion of the cap, the secondupwardly extending arm comprises a second recess and a second channel,the second recess configured to engage with the second protrusion of thecap, wherein the first and second protrusions engage with the first andsecond recesses of the first and second upwardly extending arms as thecap is rotated from a first position to a second position, wherein thecap is configured with a threaded opening for receiving a lockingelement, the locking element capable of securely holding the elongatedrod in a fixed position relative to the coupling element, wherein thecap further comprises at least one rim which extends radially outwardfrom the upper portion the cap, wherein the first channel engages withthe at least one rim of the cap and the second channel engages with theat least one rim of the cap, wherein the first channel extends along amajority of the length of an inner surface of the first upwardlyextending arms and the second channel extends along a majority of thelength of an inner surface of the second upwardly extending arms.
 8. Thespine stabilization system of claim 7, wherein the coupling body isconfigured with a first relief area in the first recess.
 9. The spinestabilization system of claim 8, wherein the first relief area comprisesa first contact surface.
 10. The spine stabilization system of claim 9,wherein the first protrusion of the cap comprises a second contactsurface.
 11. The spine stabilization system of claim 10, wherein thefirst contact surface and second contact surface abut in a secondposition to limit rotation of the cap.
 12. The spine stabilizationsystem of claim 11, wherein the first and second contact surfaces areconfigured such that there is no net outward radial force applied to thecoupling body when the cap is in the second position.
 13. The spinestabilization system of claim 7, wherein the cap is inserted into thecoupling body in a first position and may be rotated by about 90° to asecond position.
 14. The spine stabilization system of claim 7, whereinthe at least one rim of the cap is configured to frictionally cooperatewith the first and second channel of the first and second upwardlyextending arms.
 15. The spine stabilization system of claim 7, whereinthe cap comprises a lower surface configured to exert downward forceupon the elongate rod as the cap is rotated from a first position to asecond position.